diff --git a/apps/client/src/scenes/game/application/BombManager.ts b/apps/client/src/scenes/game/application/BombManager.ts
index 0b6ef4d..9ed623a 100644
--- a/apps/client/src/scenes/game/application/BombManager.ts
+++ b/apps/client/src/scenes/game/application/BombManager.ts
@@ -9,11 +9,14 @@
 import { BombController } from "@client/scenes/game/entities/bomb/BombController";
 import type { GamePlayers } from "./game.types";
 
+/** 経過時間ミリ秒を返す関数型 */
+export type ElapsedMsProvider = () => number;
+
 type BombManagerOptions = {
   worldContainer: Container;
   players: GamePlayers;
   myId: string;
-  getElapsedMs: () => number;
+  getElapsedMs: ElapsedMsProvider;
 };
 
 /** 爆弾エンティティのライフサイクルを管理する */
@@ -21,7 +24,7 @@
   private worldContainer: Container;
   private players: GamePlayers;
   private myId: string;
-  private getElapsedMs: () => number;
+  private getElapsedMs: ElapsedMsProvider;
   private bombs: BombController[] = [];
   private lastBombPlacedElapsedMs = Number.NEGATIVE_INFINITY;
 
diff --git a/apps/client/src/scenes/game/application/GameTimer.ts b/apps/client/src/scenes/game/application/GameTimer.ts
index f880cac..1670150 100644
--- a/apps/client/src/scenes/game/application/GameTimer.ts
+++ b/apps/client/src/scenes/game/application/GameTimer.ts
@@ -5,9 +5,17 @@
  */
 import { config } from "@repo/shared";
 
+/** 現在時刻ミリ秒を返す関数型 */
+export type NowMsProvider = () => number;
+
 /** ゲーム制限時間の残り秒数を管理するタイマーモデル */
 export class GameTimer {
   private gameStartTime: number | null = null;
+  private nowMsProvider: NowMsProvider;
+
+  constructor(nowMsProvider: NowMsProvider = () => Date.now()) {
+    this.nowMsProvider = nowMsProvider;
+  }
 
   public setGameStart(startTime: number) {
     this.gameStartTime = startTime;
@@ -16,7 +24,7 @@
   public getRemainingTime(): number {
     if (!this.gameStartTime) return config.GAME_CONFIG.GAME_DURATION_SEC;
 
-    const elapsedMs = Date.now() - this.gameStartTime;
+    const elapsedMs = this.nowMsProvider() - this.gameStartTime;
     const remainingSec = config.GAME_CONFIG.GAME_DURATION_SEC - elapsedMs / 1000;
 
     return Math.max(0, remainingSec);
@@ -24,6 +32,6 @@
 
   public getElapsedMs(): number {
     if (!this.gameStartTime) return 0;
-    return Math.max(0, Date.now() - this.gameStartTime);
+    return Math.max(0, this.nowMsProvider() - this.gameStartTime);
   }
 }