diff --git a/src/commands/generate/types/__tests__/command.test.ts b/src/commands/generate/types/__tests__/command.test.ts
index b88d799..bd69e22 100644
--- a/src/commands/generate/types/__tests__/command.test.ts
+++ b/src/commands/generate/types/__tests__/command.test.ts
@@ -7,20 +7,13 @@ import type {
   ManagementApiSchema,
   ManagementClientConfig,
 } from '../types.js';
+import { createSchema } from './helpers.js';
 
 const FIXTURE_CONFIG: ManagementClientConfig = {
   serviceDomain: 'test-service',
   apiKey: 'test-key',
 };
 
-function createSchema(overrides: Partial<ManagementApiSchema> = {}): ManagementApiSchema {
-  return {
-    apiFields: [],
-    customFields: [],
-    ...overrides,
-  };
-}
-
 function createHarness(
   overrides: {
     resolveOutputFilePath?: (outputOption?: string) => string;
diff --git a/src/commands/generate/types/__tests__/helpers.ts b/src/commands/generate/types/__tests__/helpers.ts
new file mode 100644
index 0000000..a65681b
--- /dev/null
+++ b/src/commands/generate/types/__tests__/helpers.ts
@@ -0,0 +1,20 @@
+import type { GenerationTarget, ManagementApiSchema } from '../types.js';
+
+export function createSchema(overrides: Partial<ManagementApiSchema> = {}): ManagementApiSchema {
+  return {
+    apiFields: [],
+    customFields: [],
+    ...overrides,
+  };
+}
+
+export function createTarget(
+  endpoint: string,
+  overrides: Partial<GenerationTarget> = {},
+): GenerationTarget {
+  return {
+    endpoint,
+    schema: createSchema(),
+    ...overrides,
+  };
+}
diff --git a/src/commands/generate/types/__tests__/type-generator.test.ts b/src/commands/generate/types/__tests__/type-generator.test.ts
index a6ea931..f5d724c 100644
--- a/src/commands/generate/types/__tests__/type-generator.test.ts
+++ b/src/commands/generate/types/__tests__/type-generator.test.ts
@@ -1,25 +1,6 @@
 import { describe, expect, it } from 'bun:test';
 import { renderDefinitionsFile } from '../type-generator.js';
-import type { GenerationTarget, ManagementApiSchema } from '../types.js';
-
-function createSchema(overrides: Partial<ManagementApiSchema> = {}): ManagementApiSchema {
-  return {
-    apiFields: [],
-    customFields: [],
-    ...overrides,
-  };
-}
-
-function createTarget(
-  endpoint: string,
-  overrides: Partial<GenerationTarget> = {},
-): GenerationTarget {
-  return {
-    endpoint,
-    schema: createSchema(),
-    ...overrides,
-  };
-}
+import { createSchema, createTarget } from './helpers.js';
 
 describe('renderDefinitionsFile', () => {
   it('endpoint 名の PascalCase が衝突しても型名を一意化する', () => {
diff --git a/src/commands/generate/types/command.ts b/src/commands/generate/types/command.ts
index 6648b37..e9d8a47 100644
--- a/src/commands/generate/types/command.ts
+++ b/src/commands/generate/types/command.ts
@@ -1,8 +1,8 @@
 import fs from 'node:fs';
 import path from 'node:path';
+import { toErrorMessage } from '../../../utils/index.js';
 import { resolveConfig, resolveOutputFilePath, resolveSingleEndpoint } from './config.js';
 import { fetchApiList, fetchApiSchema } from './management-api.js';
-import { toErrorMessage } from './shared.js';
 import { renderDefinitionsFile } from './type-generator.js';
 import type {
   ApiListItem,
diff --git a/src/commands/generate/types/config.ts b/src/commands/generate/types/config.ts
index 2cf32b0..f2f6c96 100644
--- a/src/commands/generate/types/config.ts
+++ b/src/commands/generate/types/config.ts
@@ -1,6 +1,6 @@
 import path from 'node:path';
 import { DEFAULT_OUTPUT_FILE_NAME, DEFAULT_OUTPUT_PATH } from './constants.js';
-import { toStringValue } from './shared.js';
+import { toStringValue } from '../../../utils/index.js';
 import type { GenTypesOptions, ManagementClientConfig } from './types.js';
 
 function isDeclarationFilePath(filePath: string): boolean {
@@ -18,27 +18,30 @@ export function resolveOutputFilePath(outputOption?: string): string {
   return path.join(resolvedPath, DEFAULT_OUTPUT_FILE_NAME);
 }
 
-export function resolveConfig(options: GenTypesOptions): ManagementClientConfig {
-  const serviceDomain =
-    toStringValue(options.serviceDomain) ?? toStringValue(process.env.MICROCMS_SERVICE_DOMAIN);
-  if (!serviceDomain) {
-    const envDir = process.env.__MICROCMS_CLI_ENV_DIR ?? process.cwd();
-    throw new Error(
-      'MICROCMS_SERVICE_DOMAIN is required. You can also pass --service-domain.\n' +
-        `(Searched for .env / .env.local in: ${envDir}. CWD: ${process.cwd()})`,
-    );
-  }
-
-  const apiKey = toStringValue(options.apiKey) ?? toStringValue(process.env.MICROCMS_API_KEY);
-  if (!apiKey) {
-    const envDir = process.env.__MICROCMS_CLI_ENV_DIR ?? process.cwd();
-    throw new Error(
-      'MICROCMS_API_KEY is required. You can also pass --api-key.\n' +
-        `(Searched for .env / .env.local in: ${envDir}. CWD: ${process.cwd()})`,
-    );
-  }
+function resolveRequiredConfig(
+  optionValue: string | undefined,
+  envKey: string,
+  cliFlag: string,
+): string {
+  const value = toStringValue(optionValue) ?? toStringValue(process.env[envKey]);
+  if (value) return value;
+
+  const envDir = process.env.__MICROCMS_CLI_ENV_DIR ?? process.cwd();
+  throw new Error(
+    `${envKey} is required. You can also pass ${cliFlag}.\n` +
+      `(Searched for .env / .env.local in: ${envDir}. CWD: ${process.cwd()})`,
+  );
+}
 
-  return { serviceDomain, apiKey };
+export function resolveConfig(options: GenTypesOptions): ManagementClientConfig {
+  return {
+    serviceDomain: resolveRequiredConfig(
+      options.serviceDomain,
+      'MICROCMS_SERVICE_DOMAIN',
+      '--service-domain',
+    ),
+    apiKey: resolveRequiredConfig(options.apiKey, 'MICROCMS_API_KEY', '--api-key'),
+  };
 }
 
 export function resolveSingleEndpoint(endpointId: string | undefined): string {
diff --git a/src/commands/generate/types/management-api.ts b/src/commands/generate/types/management-api.ts
index 1ef53e6..5338c6b 100644
--- a/src/commands/generate/types/management-api.ts
+++ b/src/commands/generate/types/management-api.ts
@@ -1,5 +1,5 @@
 import { MANAGEMENT_API_BASE_DOMAIN } from './constants.js';
-import { isRecord, toBooleanValue, toStringArray, toStringValue } from './shared.js';
+import { isRecord, parseArray, toBooleanValue, toStringArray, toStringValue } from '../../../utils/index.js';
 import type {
   ApiListItem,
   ManagementApiField,
@@ -90,12 +90,6 @@ function parseCustomField(rawCustomField: unknown): ManagementCustomField | null
 
   const createdAt = toStringValue(rawCustomField.createdAt);
   const fieldId = toStringValue(rawCustomField.fieldId);
-  const fields = Array.isArray(rawCustomField.fields)
-    ? rawCustomField.fields
-        .map((field) => parseApiField(field))
-        .filter((field): field is ManagementApiField => field !== null)
-    : [];
-
   if (!createdAt || !fieldId) {
     return null;
   }
@@ -103,7 +97,7 @@ function parseCustomField(rawCustomField: unknown): ManagementCustomField | null
   return {
     createdAt,
     fieldId,
-    fields,
+    fields: parseArray(rawCustomField.fields, parseApiField),
   };
 }
 
@@ -112,21 +106,9 @@ function parseApiSchema(rawSchema: unknown): ManagementApiSchema {
     throw new Error('Management API schema response is invalid.');
   }
 
-  const apiFields = Array.isArray(rawSchema.apiFields)
-    ? rawSchema.apiFields
-        .map((field) => parseApiField(field))
-        .filter((field): field is ManagementApiField => field !== null)
-    : [];
-
-  const customFields = Array.isArray(rawSchema.customFields)
-    ? rawSchema.customFields
-        .map((field) => parseCustomField(field))
-        .filter((field): field is ManagementCustomField => field !== null)
-    : [];
-
   return {
-    apiFields,
-    customFields,
+    apiFields: parseArray(rawSchema.apiFields, parseApiField),
+    customFields: parseArray(rawSchema.customFields, parseCustomField),
     apiType: toStringValue(rawSchema.apiType),
     apiEndpoint: toStringValue(rawSchema.apiEndpoint),
     apiName: toStringValue(rawSchema.apiName),
@@ -165,9 +147,7 @@ function parseApiList(rawResponse: unknown): ApiListItem[] {
   }
 
   for (const items of candidateArrays) {
-    const parsedItems = items
-      .map((item) => parseApiListItem(item))
-      .filter((item): item is ApiListItem => item !== null);
+    const parsedItems = parseArray(items, parseApiListItem);
     if (parsedItems.length > 0) {
       return parsedItems;
     }
diff --git a/src/commands/generate/types/type-generator.ts b/src/commands/generate/types/type-generator.ts
index 27827ab..1e09dc1 100644
--- a/src/commands/generate/types/type-generator.ts
+++ b/src/commands/generate/types/type-generator.ts
@@ -1,4 +1,4 @@
-import { toPascalCase, toTypePropertyName } from './shared.js';
+import { getUniqueName, toPascalCase, toTypePropertyName } from '../../../utils/index.js';
 import type { GenerationTarget, ManagementApiField, ManagementCustomField } from './types.js';
 
 interface GenerationContext {
@@ -15,19 +15,6 @@ export function normalizeApiType(apiType?: string): 'LIST' | 'OBJECT' {
   return apiType?.toUpperCase() === 'OBJECT' ? 'OBJECT' : 'LIST';
 }
 
-function getUniqueName(baseName: string, usedNames: Set<string>): string {
-  let candidate = baseName;
-  let suffix = 2;
-
-  while (usedNames.has(candidate)) {
-    candidate = `${baseName}${suffix}`;
-    suffix += 1;
-  }
-
-  usedNames.add(candidate);
-  return candidate;
-}
-
 function getUniqueTypeName(baseName: string, context: GenerationContext): string {
   return getUniqueName(baseName, context.usedCustomTypeNames);
 }
diff --git a/src/utils/__tests__/error.test.ts b/src/utils/__tests__/error.test.ts
new file mode 100644
index 0000000..0f5a73a
--- /dev/null
+++ b/src/utils/__tests__/error.test.ts
@@ -0,0 +1,31 @@
+import { describe, expect, it } from 'bun:test';
+import { toErrorMessage } from '../error.js';
+
+describe('toErrorMessage', () => {
+  it('Error オブジェクトから message を取り出す', () => {
+    expect(toErrorMessage(new Error('something failed'))).toBe('something failed');
+  });
+
+  it('文字列はそのまま返す', () => {
+    expect(toErrorMessage('raw string error')).toBe('raw string error');
+  });
+
+  it('数値は文字列に変換して返す', () => {
+    expect(toErrorMessage(42)).toBe('42');
+  });
+
+  it('null / undefined も文字列化して返す', () => {
+    expect(toErrorMessage(null)).toBe('null');
+    expect(toErrorMessage(undefined)).toBe('undefined');
+  });
+
+  it('Error のサブクラスからも message を取り出す', () => {
+    class CustomError extends Error {
+      constructor(message: string) {
+        super(message);
+        this.name = 'CustomError';
+      }
+    }
+    expect(toErrorMessage(new CustomError('custom'))).toBe('custom');
+  });
+});
diff --git a/src/utils/__tests__/naming.test.ts b/src/utils/__tests__/naming.test.ts
new file mode 100644
index 0000000..eb9481d
--- /dev/null
+++ b/src/utils/__tests__/naming.test.ts
@@ -0,0 +1,76 @@
+import { describe, expect, it } from 'bun:test';
+import { getUniqueName, toPascalCase, toTypePropertyName } from '../naming.js';
+
+describe('toPascalCase', () => {
+  it('ハイフン区切りの文字列を PascalCase に変換する', () => {
+    expect(toPascalCase('blog-post')).toBe('BlogPost');
+  });
+
+  it('アンダースコア区切りの文字列を PascalCase に変換する', () => {
+    expect(toPascalCase('blog_post')).toBe('BlogPost');
+  });
+
+  it('単一の単語の先頭を大文字にする', () => {
+    expect(toPascalCase('blog')).toBe('Blog');
+  });
+
+  it('既に PascalCase の文字列はそのまま返す', () => {
+    expect(toPascalCase('BlogPost')).toBe('BlogPost');
+  });
+
+  it('空文字列に対して "Generated" を返す', () => {
+    expect(toPascalCase('')).toBe('Generated');
+  });
+
+  it('数字始まりの場合は先頭に "T" を付与する', () => {
+    expect(toPascalCase('123abc')).toBe('T123abc');
+  });
+
+  it('記号のみの場合は "Generated" を返す', () => {
+    expect(toPascalCase('---')).toBe('Generated');
+  });
+
+  it('複数の連続する区切り文字を正しく処理する', () => {
+    expect(toPascalCase('blog--post__item')).toBe('BlogPostItem');
+  });
+});
+
+describe('toTypePropertyName', () => {
+  it('有効な識別子はそのまま返す', () => {
+    expect(toTypePropertyName('fieldId')).toBe('fieldId');
+    expect(toTypePropertyName('_private')).toBe('_private');
+    expect(toTypePropertyName('$special')).toBe('$special');
+  });
+
+  it('無効な識別子は JSON.stringify でクォートする', () => {
+    expect(toTypePropertyName('hero section')).toBe('"hero section"');
+    expect(toTypePropertyName('my-field')).toBe('"my-field"');
+    expect(toTypePropertyName('123start')).toBe('"123start"');
+  });
+});
+
+describe('getUniqueName', () => {
+  it('未使用の名前はそのまま返す', () => {
+    const used = new Set<string>();
+    expect(getUniqueName('Blog', used)).toBe('Blog');
+    expect(used.has('Blog')).toBe(true);
+  });
+
+  it('既に使用されている名前には連番サフィックスを付与する', () => {
+    const used = new Set<string>(['Blog']);
+    expect(getUniqueName('Blog', used)).toBe('Blog2');
+    expect(used.has('Blog2')).toBe(true);
+  });
+
+  it('連番が衝突する場合は次の番号を試行する', () => {
+    const used = new Set<string>(['Blog', 'Blog2', 'Blog3']);
+    expect(getUniqueName('Blog', used)).toBe('Blog4');
+  });
+
+  it('連続呼び出しで一意性を維持する', () => {
+    const used = new Set<string>();
+    expect(getUniqueName('Item', used)).toBe('Item');
+    expect(getUniqueName('Item', used)).toBe('Item2');
+    expect(getUniqueName('Item', used)).toBe('Item3');
+  });
+});
diff --git a/src/utils/__tests__/parse.test.ts b/src/utils/__tests__/parse.test.ts
new file mode 100644
index 0000000..5fc61e5
--- /dev/null
+++ b/src/utils/__tests__/parse.test.ts
@@ -0,0 +1,103 @@
+import { describe, expect, it } from 'bun:test';
+import { isRecord, parseArray, toBooleanValue, toStringArray, toStringValue } from '../parse.js';
+
+describe('isRecord', () => {
+  it('プレーンオブジェクトに対して true を返す', () => {
+    expect(isRecord({})).toBe(true);
+    expect(isRecord({ key: 'value' })).toBe(true);
+  });
+
+  it('null, 配列, プリミティブに対して false を返す', () => {
+    expect(isRecord(null)).toBe(false);
+    expect(isRecord(undefined)).toBe(false);
+    expect(isRecord([])).toBe(false);
+    expect(isRecord('string')).toBe(false);
+    expect(isRecord(42)).toBe(false);
+    expect(isRecord(true)).toBe(false);
+  });
+});
+
+describe('toStringValue', () => {
+  it('文字列を trim して返す', () => {
+    expect(toStringValue('hello')).toBe('hello');
+    expect(toStringValue('  trimmed  ')).toBe('trimmed');
+  });
+
+  it('空文字列やホワイトスペースのみなら undefined を返す', () => {
+    expect(toStringValue('')).toBeUndefined();
+    expect(toStringValue('   ')).toBeUndefined();
+  });
+
+  it('文字列以外の値に対して undefined を返す', () => {
+    expect(toStringValue(42)).toBeUndefined();
+    expect(toStringValue(null)).toBeUndefined();
+    expect(toStringValue(undefined)).toBeUndefined();
+    expect(toStringValue(true)).toBeUndefined();
+    expect(toStringValue({})).toBeUndefined();
+  });
+});
+
+describe('toBooleanValue', () => {
+  it('boolean 値をそのまま返す', () => {
+    expect(toBooleanValue(true)).toBe(true);
+    expect(toBooleanValue(false)).toBe(false);
+  });
+
+  it('boolean 以外の値に対して undefined を返す', () => {
+    expect(toBooleanValue('true')).toBeUndefined();
+    expect(toBooleanValue(1)).toBeUndefined();
+    expect(toBooleanValue(null)).toBeUndefined();
+    expect(toBooleanValue(undefined)).toBeUndefined();
+  });
+});
+
+describe('toStringArray', () => {
+  it('文字列の配列をフィルタリングして返す', () => {
+    expect(toStringArray(['a', 'b', 'c'])).toEqual(['a', 'b', 'c']);
+  });
+
+  it('非文字列要素を除外する', () => {
+    expect(toStringArray(['a', 42, 'b', null])).toEqual(['a', 'b']);
+  });
+
+  it('空文字列・ホワイトスペースのみの要素を除外する', () => {
+    expect(toStringArray(['a', '', '   ', 'b'])).toEqual(['a', 'b']);
+  });
+
+  it('有効な要素が無い場合は undefined を返す', () => {
+    expect(toStringArray([])).toBeUndefined();
+    expect(toStringArray(['', '   '])).toBeUndefined();
+  });
+
+  it('配列以外の値に対して undefined を返す', () => {
+    expect(toStringArray('not-array')).toBeUndefined();
+    expect(toStringArray(null)).toBeUndefined();
+    expect(toStringArray(undefined)).toBeUndefined();
+  });
+});
+
+describe('parseArray', () => {
+  it('各要素をパーサーで変換し、null を除外して返す', () => {
+    const parser = (item: unknown) => {
+      if (typeof item === 'number' && item > 0) return item * 2;
+      return null;
+    };
+
+    expect(parseArray([1, -1, 2, 0, 3], parser)).toEqual([2, 4, 6]);
+  });
+
+  it('配列以外の値に対して空配列を返す', () => {
+    expect(parseArray(null, () => null)).toEqual([]);
+    expect(parseArray(undefined, () => null)).toEqual([]);
+    expect(parseArray('string', () => null)).toEqual([]);
+    expect(parseArray({}, () => null)).toEqual([]);
+  });
+
+  it('全要素が null を返す場合は空配列を返す', () => {
+    expect(parseArray([1, 2, 3], () => null)).toEqual([]);
+  });
+
+  it('空配列に対して空配列を返す', () => {
+    expect(parseArray([], (x) => x as string)).toEqual([]);
+  });
+});
diff --git a/src/utils/error.ts b/src/utils/error.ts
new file mode 100644
index 0000000..56fddf6
--- /dev/null
+++ b/src/utils/error.ts
@@ -0,0 +1,3 @@
+export function toErrorMessage(error: unknown): string {
+  return error instanceof Error ? error.message : String(error);
+}
diff --git a/src/utils/index.ts b/src/utils/index.ts
new file mode 100644
index 0000000..7fa1f34
--- /dev/null
+++ b/src/utils/index.ts
@@ -0,0 +1,3 @@
+export { isRecord, parseArray, toBooleanValue, toStringArray, toStringValue } from './parse.js';
+export { getUniqueName, toPascalCase, toTypePropertyName } from './naming.js';
+export { toErrorMessage } from './error.js';
diff --git a/src/utils/naming.ts b/src/utils/naming.ts
new file mode 100644
index 0000000..0c5aefb
--- /dev/null
+++ b/src/utils/naming.ts
@@ -0,0 +1,24 @@
+export function toPascalCase(value: string): string {
+  const chunks = value.split(/[^A-Za-z0-9]+/).filter((chunk) => chunk.length > 0);
+  const raw = chunks.map((chunk) => `${chunk.charAt(0).toUpperCase()}${chunk.slice(1)}`).join('');
+
+  const safe = raw.length > 0 ? raw : 'Generated';
+  return /^[A-Za-z_$]/.test(safe) ? safe : `T${safe}`;
+}
+
+export function toTypePropertyName(value: string): string {
+  return /^[A-Za-z_$][A-Za-z0-9_$]*$/.test(value) ? value : JSON.stringify(value);
+}
+
+export function getUniqueName(baseName: string, usedNames: Set<string>): string {
+  let candidate = baseName;
+  let suffix = 2;
+
+  while (usedNames.has(candidate)) {
+    candidate = `${baseName}${suffix}`;
+    suffix += 1;
+  }
+
+  usedNames.add(candidate);
+  return candidate;
+}
diff --git a/src/commands/generate/types/shared.ts b/src/utils/parse.ts
similarity index 56%
rename from src/commands/generate/types/shared.ts
rename to src/utils/parse.ts
index 9f5e52f..61c5dac 100644
--- a/src/commands/generate/types/shared.ts
+++ b/src/utils/parse.ts
@@ -26,18 +26,7 @@ export function toStringArray(value: unknown): string[] | undefined {
   return values.length > 0 ? values : undefined;
 }
 
-export function toPascalCase(value: string): string {
-  const chunks = value.split(/[^A-Za-z0-9]+/).filter((chunk) => chunk.length > 0);
-  const raw = chunks.map((chunk) => `${chunk.charAt(0).toUpperCase()}${chunk.slice(1)}`).join('');
-
-  const safe = raw.length > 0 ? raw : 'Generated';
-  return /^[A-Za-z_$]/.test(safe) ? safe : `T${safe}`;
-}
-
-export function toTypePropertyName(value: string): string {
-  return /^[A-Za-z_$][A-Za-z0-9_$]*$/.test(value) ? value : JSON.stringify(value);
-}
-
-export function toErrorMessage(error: unknown): string {
-  return error instanceof Error ? error.message : String(error);
+export function parseArray<T>(rawArray: unknown, parser: (item: unknown) => T | null): T[] {
+  if (!Array.isArray(rawArray)) return [];
+  return rawArray.map(parser).filter((item): item is T => item !== null);
 }