diff --git a/src/app/app.ts b/src/app/app.ts
index 03de666..150ccc4 100644
--- a/src/app/app.ts
+++ b/src/app/app.ts
@@ -57,6 +57,7 @@ export class App {
     this.contentElement()!.nativeElement.tabIndex = 0;
     this.contentElement()!.nativeElement.focus();
 
-    this.contentElement()!.nativeElement.tabIndex = -1;
+    // @ts-ignore
+    this.contentElement()!.nativeElement.tabIndex = undefined;
   }
 }
diff --git a/src/app/features/header-menu/header-menu.html b/src/app/features/header-menu/header-menu.html
index 8e09e12..c4cd404 100644
--- a/src/app/features/header-menu/header-menu.html
+++ b/src/app/features/header-menu/header-menu.html
@@ -1,21 +1,29 @@
-<div class="menu-left">
+<div #menuLeft class="menu-left">
   <a class="brand" [routerLink]="['/']">
     <img [src]="settings.darkMode() ? '/logo.svg' : '/logo_inverted.svg'" alt="logo" height="20" width="59.52" />
-    <span #brandText [class.hidden]="!hasExtraSpace()">
+    <span #brandText [class.hidden]="expandStage() < 2">
       <strong>ADOFAI Editor Forum</strong>
     </span>
   </a>
 
-  <a class="menu-item nav-link" [routerLink]="['/levels']">{{ translation.menu.levels }}</a>
-  <span class="menu-item dummy-link">{{ translation.menu.community }}</span>
-  <span class="menu-item dummy-link">{{ translation.menu.leaderboard }}</span>
-  <span class="menu-item dummy-link">{{ translation.menu.about }}</span>
+  <div #leftMenuItems [class.hidden]="expandStage() < 1" [attr.inert]="expandStage() < 1 ? '' : null" class="menu-items">
+    <a class="menu-item nav-link" [routerLink]="['/levels']">{{ translation.menu.levels }}</a>
+    <span class="menu-item dummy-link">{{ translation.menu.community }}</span>
+    <span class="menu-item dummy-link">{{ translation.menu.leaderboard }}</span>
+    <span class="menu-item dummy-link">{{ translation.menu.about }}</span>
+  </div>
 </div>
 
-<div class="menu-right" #menuRight>
-  <a class="menu-item nav-link" [routerLink]="['/known-issues']">{{ translation.menu.knownIssues }}</a>
-  <span class="menu-item dummy-link"><strong>{{ translation.menu.login }}</strong></span>
-  <span class="menu-item dummy-link">{{ translation.menu.signup }}</span>
+<div #menuRight class="menu-right">
+  <div #rightMenuItems [class.hidden]="expandStage() < 1" [attr.inert]="expandStage() < 1 ? '' : null" class="menu-items">
+    <a class="menu-item nav-link" [routerLink]="['/known-issues']">{{ translation.menu.knownIssues }}</a>
+    <span class="menu-item dummy-link"><strong>{{ translation.menu.login }}</strong></span>
+    <span class="menu-item dummy-link">{{ translation.menu.signup }}</span>
+  </div>
+
+  <button type="button" [class.hidden]="expandStage() > 0" [attr.inert]="expandStage() > 0 ? '' : null" class="material-symbols-outlined icon-40 menu" (click)="onHamburgerClick()" [attr.aria-label]="translation.menu.menu">
+    menu
+  </button>
 
   <button type="button" class="material-symbols-outlined icon-40 settings" (click)="onSettingsClick()" [attr.aria-label]="translation.settings.title">
     settings
diff --git a/src/app/features/header-menu/header-menu.scss b/src/app/features/header-menu/header-menu.scss
index b90e026..7d71164 100644
--- a/src/app/features/header-menu/header-menu.scss
+++ b/src/app/features/header-menu/header-menu.scss
@@ -4,11 +4,12 @@
   display: flex;
   flex-direction: row;
   align-items: center;
-  justify-content: start;
+  justify-content: space-between;
   gap: 0;
 
   width: fit-content;
   min-width: 100%;
+  height: 64px;
 
   box-sizing: border-box;
   box-shadow: 0 2px 0 light-dark(oklch(0 0 0 / 20%), oklch(1 0 0 / 20%));
@@ -26,11 +27,24 @@
     align-items: center;
     gap: 48px;
 
+    .menu-items {
+      display: flex;
+      flex-direction: row;
+      align-items: center;
+      gap: 48px;
+
+      &.hidden {
+        position: absolute;
+        top: -100000px;
+        pointer-events: none;
+      }
+    }
+
     & > * {
       user-select: none;
     }
 
-    .menu-item, a:not(.settings) {
+    .menu-item, a {
       text-decoration: none;
       font-size: 18px;
       height: 40px;
@@ -62,7 +76,7 @@
       }
     }
 
-    .settings {
+    .settings, .menu {
       border: none;
       border-radius: 100%;
       background-color: inherit;
@@ -71,6 +85,9 @@
       position: relative;
       z-index: 10;
       cursor: pointer;
+    }
+
+    .settings {
       transition: transform 0.3s ease;
 
       &:hover {
@@ -78,6 +95,14 @@
       }
     }
 
+    .menu {
+      &.hidden {
+        position: absolute;
+        top: -100000px;
+        pointer-events: none;
+      }
+    }
+
     /* 구체적인 아이콘 예외 처리 */
     .icon-40 {
       height: auto;
@@ -85,6 +110,9 @@
   }
 
   .menu-left {
+    position: absolute;
+    left: 0;
+
     justify-content: start;
     padding: 12px;
 
@@ -104,7 +132,7 @@
       img {
         display: inline-block;
         height: 20px;
-        padding: 10px 10px 10px 0;
+        padding: 10px 0;
       }
 
       strong {
@@ -113,9 +141,11 @@
 
       span {
         display: inline-block;
+        padding-left: 10px;
 
         &.hidden {
-          display: none;
+          position: absolute;
+          top: -100000px;
           pointer-events: none;
         }
       }
@@ -123,8 +153,10 @@
   }
 
   .menu-right {
-    flex-grow: 1;
+    position: absolute;
+    right: 0;
+
     justify-content: flex-end;
-    padding: 12px 20px;
+    padding: 12px 20px 12px 12px;
   }
 }
diff --git a/src/app/features/header-menu/header-menu.ts b/src/app/features/header-menu/header-menu.ts
index e132ff4..3e232e5 100644
--- a/src/app/features/header-menu/header-menu.ts
+++ b/src/app/features/header-menu/header-menu.ts
@@ -6,6 +6,7 @@ import {
   inject,
   NgZone,
   OnDestroy,
+  OnInit,
   signal,
   viewChild,
 } from '@angular/core';
@@ -21,101 +22,132 @@ import { SettingsService } from '../../services/settings.service';
   templateUrl: './header-menu.html',
   styleUrl: './header-menu.scss',
   changeDetection: ChangeDetectionStrategy.OnPush,
+  host: {
+    '[class.folded-menu]': 'expandStage() < 1',
+  },
 })
 export class HeaderMenu implements OnDestroy {
   private popupService = inject(PopupService);
   protected translation = inject(TranslationService).translation;
   protected settings = inject(SettingsService);
 
-  menuRight = viewChild<ElementRef<HTMLElement>>('menuRight');
-  brandText = viewChild<ElementRef<HTMLElement>>('brandText');
+  private static readonly LOGICAL_GAP = 24;
 
-  hasExtraSpace = signal(true);
+  private resizeObserver?: ResizeObserver;
+  private brandTextObserver?: ResizeObserver;
+  private menuItemsObserver?: ResizeObserver;
+  private menuWidth: number = 99999;
 
-  private menuResizeObserver: ResizeObserver | null = null;
-  private textResizeObserver: ResizeObserver | null = null;
+  private menuLeft = viewChild<ElementRef<HTMLElement>>('menuLeft');
+  private leftMenuItems = viewChild<ElementRef<HTMLElement>>('leftMenuItems');
+  private menuLeftWidth: number = 0;
+  private leftMenuItemsWidth: number = 0;
 
-  private childWidths = new Map<Element, number>();
-  private cachedTextWidth = 0;
-  private cachedRightMenuContentWidth = 0;
+  private menuRight = viewChild<ElementRef<HTMLElement>>('menuRight');
+  private rightMenuItems = viewChild<ElementRef<HTMLElement>>('rightMenuItems');
+  private menuRightWidth: number = 0;
+  private rightMenuItemsWidth: number = 0;
 
-  constructor(private ngZone: NgZone) {
+  private brandText = viewChild<ElementRef<HTMLElement>>('brandText');
+  private brandTextWidth: number = 0;
+
+  expandStage = signal(2);
+
+  constructor(
+    private element: ElementRef,
+    private ngZone: NgZone,
+  ) {
     afterNextRender(() => {
-      const rightElement = this.menuRight()?.nativeElement;
-      const textElement = this.brandText()?.nativeElement;
-      if (!rightElement || !textElement) return;
-
       this.ngZone.runOutsideAngular(() => {
-        // 1. Right Menu & Children Observer
-        this.menuResizeObserver = new ResizeObserver((entries) => {
-          let containerWidth = -1;
-          let contentChanged = false;
-
-          for (const entry of entries) {
-            if (entry.target === rightElement) {
-              containerWidth = entry.borderBoxSize[0].inlineSize;
-              continue;
-            }
-
+        this.resizeObserver = new ResizeObserver((entries) => {
+          for (let entry of entries) {
             const width = entry.borderBoxSize[0].inlineSize;
-            if (this.childWidths.get(entry.target) !== width) {
-              this.childWidths.set(entry.target, width);
-              contentChanged = true;
-            }
+            if (width > 0)
+              switch (entry.target) {
+                case element.nativeElement:
+                  this.menuWidth = width;
+                  break;
+                case this.menuLeft()!.nativeElement:
+                  this.menuLeftWidth = width;
+                  break;
+                case this.menuRight()!.nativeElement:
+                  this.menuRightWidth = width;
+                  break;
+              }
           }
 
-          if (contentChanged) this.updateCachedRightMenuContentWidth();
-          if (containerWidth !== -1) this.resize(containerWidth);
+          this.updateExpandStatus();
         });
 
-        this.menuResizeObserver.observe(rightElement);
-        Array.from(rightElement.children).forEach((child) => {
-          this.childWidths.set(child, (child as HTMLElement).offsetWidth);
-          this.menuResizeObserver?.observe(child);
+        this.menuItemsObserver = new ResizeObserver((entries) => {
+          for (let entry of entries) {
+            const width = entry.borderBoxSize[0].inlineSize;
+            if (width > 0)
+              switch (entry.target) {
+                case this.leftMenuItems()!.nativeElement:
+                  this.leftMenuItemsWidth = width;
+                  break;
+                case this.rightMenuItems()!.nativeElement:
+                  this.rightMenuItemsWidth = width;
+                  break;
+              }
+          }
+
+          this.updateExpandStatus();
         });
 
-        // 2. Brand Text Observer
-        this.textResizeObserver = new ResizeObserver((entries) => {
+        this.resizeObserver.observe(element.nativeElement);
+        this.resizeObserver.observe(this.menuLeft()!.nativeElement);
+        this.resizeObserver.observe(this.menuRight()!.nativeElement);
+
+        this.menuItemsObserver.observe(this.leftMenuItems()!.nativeElement);
+        this.menuItemsObserver.observe(this.rightMenuItems()!.nativeElement);
+
+        this.brandTextObserver = new ResizeObserver((entries) => {
           const width = entries[0].borderBoxSize[0].inlineSize;
-          if (width > 0) this.cachedTextWidth = width;
+          if (width > 0) this.brandTextWidth = width;
+
+          this.updateExpandStatus();
         });
 
-        this.textResizeObserver.observe(textElement);
-
-        // Initial calculation
-        this.cachedTextWidth = textElement.offsetWidth;
-        this.updateCachedRightMenuContentWidth();
-        this.resize(rightElement.offsetWidth);
+        this.brandTextObserver.observe(this.brandText()!.nativeElement);
       });
     });
   }
 
   ngOnDestroy() {
-    this.menuResizeObserver?.disconnect();
-    this.textResizeObserver?.disconnect();
-    this.childWidths.clear();
+    this.resizeObserver?.disconnect();
+    this.menuItemsObserver?.disconnect();
+    this.brandTextObserver?.disconnect();
   }
 
-  private updateCachedRightMenuContentWidth() {
-    const gap = 48;
-    const widths = Array.from(this.childWidths.values());
-    if (widths.length === 0) {
-      this.cachedRightMenuContentWidth = 0;
-      return;
-    }
+  private updateExpandStatus() {
+    let menuContentWidth = this.menuLeftWidth + this.menuRightWidth;
+    let enoughSpace = this.menuWidth > menuContentWidth + HeaderMenu.LOGICAL_GAP;
+    let initialExpandStage = this.expandStage();
 
-    this.cachedRightMenuContentWidth =
-      widths.reduce((acc, w) => acc + w, 0) + (widths.length - 1) * gap;
+    if (enoughSpace) {
+      let extraSpaceToExpand = Number.MAX_VALUE;
+      switch (initialExpandStage) {
+        case 1:
+          extraSpaceToExpand = this.brandTextWidth;
+          break;
+        case 0:
+          extraSpaceToExpand = this.leftMenuItemsWidth + this.rightMenuItemsWidth + 48 - 40;
+          break;
+      }
+
+      if (
+        // Add a gap of 2px to prevent flickering
+        this.menuWidth >= menuContentWidth + HeaderMenu.LOGICAL_GAP + extraSpaceToExpand + 2
+      ) {
+        this.expandStage.set(initialExpandStage + 1);
+      }
+    } else if (initialExpandStage > 0) this.expandStage.set(initialExpandStage - 1);
   }
 
-  private resize(availableWidth: number) {
-    const hadSpace = this.hasExtraSpace();
+  onHamburgerClick(): void {
 
-    const buffer = 20 * 2 + 24; // Internal Padding + Logical Gap
-    const threshold = hadSpace ? 0 : this.cachedTextWidth;
-    const hasSpace = availableWidth > this.cachedRightMenuContentWidth + threshold + buffer;
-
-    if (hadSpace !== hasSpace) this.ngZone.run(() => this.hasExtraSpace.set(hasSpace));
   }
 
   onSettingsClick() {
diff --git a/src/app/i18n/en.ts b/src/app/i18n/en.ts
index 9d8a7ca..8574296 100644
--- a/src/app/i18n/en.ts
+++ b/src/app/i18n/en.ts
@@ -16,6 +16,7 @@ export const EN = {
     knownIssues: 'Known Issues',
     login: 'Login',
     signup: 'Signup',
+    menu: 'Menu',
   },
   common: {
     selectOption: 'Select Option...',
diff --git a/src/app/i18n/jp.ts b/src/app/i18n/jp.ts
index ac7a06d..09d725f 100644
--- a/src/app/i18n/jp.ts
+++ b/src/app/i18n/jp.ts
@@ -18,6 +18,7 @@ export const JP: Translation = {
     knownIssues: '既知の問題',
     login: 'ログイン',
     signup: '新規登録',
+    menu: 'メニュー',
   },
   common: {
     selectOption: 'オプションを選択...',
diff --git a/src/app/i18n/kr.ts b/src/app/i18n/kr.ts
index cc476bd..9480bae 100644
--- a/src/app/i18n/kr.ts
+++ b/src/app/i18n/kr.ts
@@ -18,6 +18,7 @@ export const KR: Translation = {
     knownIssues: '알려진 문제',
     login: '로그인',
     signup: '회원가입',
+    menu: '메뉴',
   },
   common: {
     selectOption: '옵션 선택...',