diff --git a/packages/app-common/src/apis/app/apis.ts b/packages/app-common/src/apis/app/apis.ts
index d3e7a262..cdfb86a5 100644
--- a/packages/app-common/src/apis/app/apis.ts
+++ b/packages/app-common/src/apis/app/apis.ts
@@ -7,7 +7,7 @@ export enum AppAPIChannel {
     GET_APP_DETAILS = 'App_GetAppDetails',
 }
 
-type CreateWindowAPI = IpcRendererInvokerAPI<(windowType: WindowType) => void>;
+type CreateWindowAPI = IpcRendererInvokerAPI<(type: WindowType) => void>;
 type GetAppDetails = IpcRendererInvokerAPI<() => AppDetails>;
 
 export interface AppMainAPI {
diff --git a/packages/app-main/src/main/apis/app/index.ts b/packages/app-main/src/main/apis/app/index.ts
index 16c578fa..393bf414 100644
--- a/packages/app-main/src/main/apis/app/index.ts
+++ b/packages/app-main/src/main/apis/app/index.ts
@@ -3,10 +3,10 @@ import { AppAPIChannel } from '@ter/app-common/apis/app';
 import { ipcMain } from 'electron';
 
 import { getAppDetails } from 'src/main/app';
-import { windowManager } from 'src/main/window';
+import { WindowManager } from 'src/main/window';
 
 function registerCreateWindowHandler() {
-    const handler: AppMainAPI['handleCreateWindow'] = (_, windowType) => windowManager.createWindow({ windowType });
+    const handler: AppMainAPI['handleCreateWindow'] = (_, type) => WindowManager.INSTANCE.createWindow({ type });
     ipcMain.handle(AppAPIChannel.CREATE_WINDOW, handler);
 }
 
diff --git a/packages/app-main/src/main/index.ts b/packages/app-main/src/main/index.ts
index cc527f43..b6b0ae10 100644
--- a/packages/app-main/src/main/index.ts
+++ b/packages/app-main/src/main/index.ts
@@ -2,7 +2,7 @@ import { WindowType } from '@ter/app-common/apis/app';
 import { app, BrowserWindow } from 'electron';
 
 import { registerAppGlobalHandlers } from './apis/app';
-import { windowManager } from './window';
+import { WindowManager } from './window';
 
 async function installExtensions(): Promise<void> {
     const {
@@ -29,7 +29,7 @@ async function handleReady() {
 
     registerAppGlobalHandlers();
 
-    windowManager.createWindow({ windowType: WindowType.MAIN });
+    WindowManager.INSTANCE.createWindow({ type: WindowType.MAIN });
 }
 
 // This method will be called when Electron has finished initialization and is ready to create browser windows.
@@ -48,6 +48,6 @@ app.on('activate', () => {
     // On macOS, usually applications will re-create new windows if single click the dock icon when no other windows
     // opened.
     if (BrowserWindow.getAllWindows().length === 0) {
-        windowManager.createWindow({ windowType: WindowType.MAIN });
+        WindowManager.INSTANCE.createWindow({ type: WindowType.MAIN });
     }
 });
diff --git a/packages/app-main/src/main/window/abstractWindow.ts b/packages/app-main/src/main/window/abstractWindow.ts
index cfb13261..9fab2383 100644
--- a/packages/app-main/src/main/window/abstractWindow.ts
+++ b/packages/app-main/src/main/window/abstractWindow.ts
@@ -11,15 +11,13 @@ import type { AbstractWindowOption, CloseWindowOption } from './types';
 export abstract class AbstractWindow {
     protected declare readonly _window: BrowserWindow;
     protected declare readonly _windowType: WindowType;
-    protected declare readonly _windowId: string;
 
     private declare readonly _onClose: (option: CloseWindowOption) => void | Promise<void>;
 
     constructor(option: AbstractWindowOption) {
-        this._windowId = option.windowId;
-        this._windowType = option.windowType;
+        this._windowType = option.type;
 
-        const windowStateKeeper = new WindowStateKeeper(option.windowType);
+        const windowStateKeeper = new WindowStateKeeper(this._windowType);
 
         this._window = new BrowserWindow({
             x: windowStateKeeper.x,
@@ -42,6 +40,10 @@ export abstract class AbstractWindow {
         this._addAPIHandlers();
     }
 
+    get id() {
+        return this._window.id;
+    }
+
     async show(): Promise<void> {
         if (process.env.NODE_ENV === 'production') {
             await this._window.loadFile(path.resolve(appPaths.src, 'index.html'));
@@ -66,7 +68,7 @@ export abstract class AbstractWindow {
     private _close = () => {
         this._removeAPIHandlers();
 
-        void this._onClose({ windowId: this._windowId });
+        void this._onClose({ id: this.id });
     };
 
     // ---------------------------------------------------------------------------------------------------- Ipc Handlers
diff --git a/packages/app-main/src/main/window/mainWindow.ts b/packages/app-main/src/main/window/mainWindow.ts
index 727dcc01..ceb59cac 100644
--- a/packages/app-main/src/main/window/mainWindow.ts
+++ b/packages/app-main/src/main/window/mainWindow.ts
@@ -5,6 +5,6 @@ import type { WindowOption } from './types';
 
 export class MainWindow extends AbstractWindow {
     constructor(option: WindowOption) {
-        super({ windowType: WindowType.MAIN, ...option });
+        super({ type: WindowType.MAIN, ...option });
     }
 }
diff --git a/packages/app-main/src/main/window/types.ts b/packages/app-main/src/main/window/types.ts
index 579e3034..dea64a56 100644
--- a/packages/app-main/src/main/window/types.ts
+++ b/packages/app-main/src/main/window/types.ts
@@ -1,18 +1,17 @@
 import type { WindowType } from '@ter/app-common/apis/app';
 
 export interface CreateWindowOption {
-    windowType: WindowType;
+    type: WindowType;
 }
 
 export interface CloseWindowOption {
-    windowId: string;
+    id: number;
 }
 
 export interface WindowOption {
-    windowId: string;
     onClose: (option: CloseWindowOption) => void | Promise<void>;
 }
 
 export interface AbstractWindowOption extends WindowOption {
-    windowType: WindowType;
+    type: WindowType;
 }
diff --git a/packages/app-main/src/main/window/windowManager.ts b/packages/app-main/src/main/window/windowManager.ts
index 3cc2c1d0..093c9ca8 100644
--- a/packages/app-main/src/main/window/windowManager.ts
+++ b/packages/app-main/src/main/window/windowManager.ts
@@ -7,47 +7,44 @@ import type { AbstractWindow } from './abstractWindow';
 import { MainWindow } from './mainWindow';
 import type { CloseWindowOption, CreateWindowOption } from './types';
 
-interface WindowStore {
-    [id: string]: Nullable<AbstractWindow>;
-}
+type WindowStore = Record<number, Nullable<AbstractWindow>>;
 
 export class WindowManager {
-    private declare _count: number;
-    private declare _store: WindowStore;
+    private declare static _instance?: WindowManager;
 
-    constructor() {
-        this._count = 0;
-        this._store = {};
+    static get INSTANCE() {
+        if (!WindowManager._instance) {
+            WindowManager._instance = new WindowManager();
+        }
+        return WindowManager._instance;
     }
 
-    createWindow = (option: CreateWindowOption): void => {
-        this._count++;
+    private declare _store: WindowStore;
 
-        const { windowType } = option;
-        const windowId = `${windowType}-${this._count}`;
+    private constructor() {
+        this._store = {};
+    }
 
-        switch (windowType) {
+    private _newWindow(type: WindowType): AbstractWindow {
+        switch (type) {
             case WindowType.MAIN:
-                this._store[windowId] = new MainWindow({
-                    windowId,
+                return new MainWindow({
                     onClose: this._closeWindow,
                 });
-                break;
 
             /* istanbul ignore next */
             default:
-                assertIsNever(windowType);
+                assertIsNever(type);
         }
+    }
 
-        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-        void this._store[windowId]!.show();
-    };
+    createWindow(option: CreateWindowOption): void {
+        const window = this._newWindow(option.type);
+        this._store[window.id] = window;
+        void window.show();
+    }
 
     private _closeWindow = (option: CloseWindowOption): void => {
-        const { windowId } = option;
-
-        this._store[windowId] = null;
+        this._store[option.id] = null;
     };
 }
-
-export const windowManager = new WindowManager();