diff --git a/core/src/activity-utils/makeActivityReducer.spec.ts b/core/src/activity-utils/makeActivityReducer.spec.ts
new file mode 100644
index 000000000..f81adf8ff
--- /dev/null
+++ b/core/src/activity-utils/makeActivityReducer.spec.ts
@@ -0,0 +1,58 @@
+import { makeEvent } from "../event-utils";
+import type { Activity } from "../Stack";
+import { makeActivityReducer } from "./makeActivityReducer";
+
+function makeActivity(): Activity {
+  const pushedEvent = makeEvent("Pushed", {
+    activityId: "a1",
+    activityName: "sample",
+    activityParams: { page: "1" },
+  });
+
+  const stepPushedEvent = makeEvent("StepPushed", {
+    stepId: "s2",
+    stepParams: { page: "2" },
+  });
+
+  return {
+    id: "a1",
+    name: "sample",
+    transitionState: "enter-done",
+    params: { page: "2" },
+    enteredBy: pushedEvent,
+    steps: [
+      {
+        id: "a1",
+        params: { page: "1" },
+        enteredBy: pushedEvent,
+        zIndex: -1,
+      },
+      {
+        id: "s2",
+        params: { page: "2" },
+        enteredBy: stepPushedEvent,
+        zIndex: -1,
+      },
+    ],
+    isTop: true,
+    isActive: true,
+    isRoot: true,
+    zIndex: 0,
+  };
+}
+
+test("makeActivityReducer - StepPopped는 activity.steps를 변경하지 않고 새 배열을 반환합니다", () => {
+  const activity = makeActivity();
+  const originalSteps = activity.steps;
+
+  const reducer = makeActivityReducer({ transitionDuration: 300, now: 0 });
+  const stepPoppedEvent = makeEvent("StepPopped", {});
+
+  const nextActivity = reducer(activity, stepPoppedEvent);
+
+  expect(activity.steps).toBe(originalSteps);
+  expect(activity.steps.length).toBe(2);
+  expect(nextActivity.steps).not.toBe(originalSteps);
+  expect(nextActivity.steps.length).toBe(1);
+  expect(nextActivity.params).toEqual({ page: "1" });
+});
diff --git a/core/src/activity-utils/makeActivityReducer.ts b/core/src/activity-utils/makeActivityReducer.ts
index fac85e2d7..1bdb0e989 100644
--- a/core/src/activity-utils/makeActivityReducer.ts
+++ b/core/src/activity-utils/makeActivityReducer.ts
@@ -108,13 +108,14 @@ export function makeActivityReducer(context: {
      * If there are params in the previous step, set them as the new params
      */
     StepPopped: (activity: Activity, event: StepPoppedEvent): Activity => {
-      activity.steps.pop();
+      const steps = activity.steps.slice(0, -1);
 
-      const beforeActivityParams = last(activity.steps)?.params;
+      const beforeActivityParams = last(steps)?.params;
 
       return {
         ...activity,
         params: beforeActivityParams ?? activity.params,
+        steps,
       };
     },
 
diff --git a/core/src/activity-utils/makeReducer.spec.ts b/core/src/activity-utils/makeReducer.spec.ts
new file mode 100644
index 000000000..62c57fbf0
--- /dev/null
+++ b/core/src/activity-utils/makeReducer.spec.ts
@@ -0,0 +1,50 @@
+import type { DomainEvent } from "../event-types";
+import { makeReducer } from "./makeReducer";
+
+test("makeReducer - 등록된 이벤트는 해당 reducer로 처리됩니다", () => {
+  const reducer = makeReducer<number>({
+    Initialized: (state) => state + 1,
+    ActivityRegistered: (state) => state,
+    Pushed: (state) => state,
+    Replaced: (state) => state,
+    Popped: (state) => state,
+    StepPushed: (state) => state,
+    StepReplaced: (state) => state,
+    StepPopped: (state) => state,
+    Paused: (state) => state,
+    Resumed: (state) => state,
+  });
+
+  const event = {
+    id: "e1",
+    name: "Initialized",
+    eventDate: 0,
+  } as unknown as DomainEvent;
+
+  expect(reducer(0, event)).toBe(1);
+});
+
+test("makeReducer - 등록되지 않은 이벤트는 명확한 에러를 던집니다", () => {
+  const reducer = makeReducer<number>({
+    Initialized: (state) => state,
+    ActivityRegistered: (state) => state,
+    Pushed: (state) => state,
+    Replaced: (state) => state,
+    Popped: (state) => state,
+    StepPushed: (state) => state,
+    StepReplaced: (state) => state,
+    StepPopped: (state) => state,
+    Paused: (state) => state,
+    Resumed: (state) => state,
+  });
+
+  const unknownEvent = {
+    id: "e1",
+    name: "Unknown",
+    eventDate: 0,
+  } as unknown as DomainEvent;
+
+  expect(() => reducer(0, unknownEvent)).toThrow(
+    `No reducer for event ${JSON.stringify(unknownEvent)}`,
+  );
+});
diff --git a/core/src/activity-utils/makeReducer.ts b/core/src/activity-utils/makeReducer.ts
index 5c5c2d285..d6c7f9a91 100644
--- a/core/src/activity-utils/makeReducer.ts
+++ b/core/src/activity-utils/makeReducer.ts
@@ -11,10 +11,10 @@ export function makeReducer<T>(
   },
 ) {
   return (target: T, event: DomainEvent) => {
-    const reducer = (reducerMap[event.name] as Reducer<T>).bind(reducerMap);
-    if (reducer) {
-      return reducer(target, event);
+    const rawReducer = reducerMap[event.name] as Reducer<T> | undefined;
+    if (!rawReducer) {
+      throw new Error(`No reducer for event ${JSON.stringify(event)}`);
     }
-    throw new Error(`No reducer for event ${JSON.stringify(event)}`);
+    return rawReducer.bind(reducerMap)(target, event);
   };
 }