diff --git a/frontend/src/components/MenuSeparator.tsx b/frontend/src/components/MenuSeparator.tsx
new file mode 100644
index 0000000..43b94a7
--- /dev/null
+++ b/frontend/src/components/MenuSeparator.tsx
@@ -0,0 +1,6 @@
+export default () => (
+    <>
+      <span className="hidden md:inline flex items-center px-2">|</span>
+      <hr className="block md:hidden w-full opacity-25
+		     border-t border-black dark:border-white" />
+    </>)
diff --git a/frontend/src/components/TopNav.tsx b/frontend/src/components/TopNav.tsx
index db23f4a..4702f83 100644
--- a/frontend/src/components/TopNav.tsx
+++ b/frontend/src/components/TopNav.tsx
@@ -1,8 +1,9 @@
 import axios from 'axios'
 import toCamel from 'camelcase-keys'
 import { useState, useEffect } from 'react'
-import { Link, useLocation, /* useNavigate */ } from 'react-router-dom'
+import { Link, useLocation, useNavigate } from 'react-router-dom'
 
+import Separator from '@/components/MenuSeparator'
 import { API_BASE_URL } from '@/config'
 import { WikiIdBus } from '@/lib/eventBus/WikiIdBus'
 import { cn } from '@/lib/utils'
@@ -14,16 +15,12 @@ type Props = { user: User | null }
 
 export default ({ user }: Props) => {
   const location = useLocation ()
-  // const navigate = useNavigate ()
+  const navigate = useNavigate ()
 
-  // const [activeIndex, setActiveIndex] = useState (-1)
+  const [menuOpen, setMenuOpen] = useState (false)
+  const [openItemIdx, setOpenItemIdx] = useState (-1)
   const [postCount, setPostCount] = useState<number | null> (null)
-  // const [suggestionsVsbl, setSuggestionsVsbl] = useState (false)
-  // const [suggestions, setSuggestions] = useState<WikiPage[]> ([])
-  // const [tagSearch, setTagSearch] = useState ('')
-  // const [userSearch, setUserSearch] = useState ('')
   const [wikiId, setWikiId] = useState<number | null> (WikiIdBus.get ())
-  // const [wikiSearch, setWikiSearch] = useState ('')
 
   const wikiPageFlg = Boolean (/^\/wiki\/(?!new|changes)[^\/]+/.test (location.pathname) && wikiId)
   const wikiTitle = location.pathname.split ('/')[2]
@@ -44,8 +41,7 @@ export default ({ user }: Props) => {
 	  { name: '新規', to: '/wiki/new' },
 	  { name: '全体履歴', to: '/wiki/changes' },
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:Wiki' },
-	  { component: <span className="flex items-center px-2">|</span>,
-	    visible: wikiPageFlg },
+	  { component: <Separator />, visible: wikiPageFlg },
 	  { name: `広場 (${ postCount || 0 })`, to: `/posts?tags=${ wikiTitle }`,
 	    visible: wikiPageFlg },
 	  { name: '履歴', to: `/wiki/changes?id=${ wikiId }`, visible: wikiPageFlg },
@@ -55,61 +51,16 @@ export default ({ user }: Props) => {
 	  { name: 'お前', to: `/users/${ user?.id }`, visible: false },
 	  { name: '設定', to: '/users/settings', visible: Boolean (user) }] }]
 
-//  const whenTagSearchChanged = (ev: React.ChangeEvent<HTMLInputElement>) => {
-//    // TODO: 実装
-//
-//    setTagSearch (ev.target.value)
-//
-//    const q: string = ev.target.value.split (' ').at (-1)
-//    if (!(q))
-//      {
-//	// setSuggestions ([])
-//	return
-//      }
-//  }
-
-//  const whenWikiSearchChanged = (ev: React.ChangeEvent<HTMLInputElement>) => {
-//    // TODO: 実装
-//
-//    setWikiSearch (ev.target.value)
-//
-//    const q: string = ev.target.value.split (' ').at (-1)
-//    if (!(q))
-//      {
-//	// setSuggestions ([])
-//	return
-//      }
-//  }
-
-//  const whenUserSearchChanged = (ev: React.ChangeEvent<HTMLInputElement>) => {
-//    // TODO: 実装
-//
-//    setUserSearch (ev.target.value)
-//
-//    const q: string = ev.target.value.split (' ').at (-1)
-//    if (!(q))
-//      {
-//	// setSuggestions ([])
-//	return
-//      }
-//  }
-
-//  const handleKeyDown = (ev: React.KeyboardEvent<HTMLInputElement>) => {
-//     if (ev.key === 'Enter' && wikiSearch.length && (!(suggestionsVsbl) || activeIndex < 0))
-//       {
-//	navigate (`/wiki/${ encodeURIComponent (wikiSearch) }`)
-//	setSuggestionsVsbl (false)
-//       }
-//  }
-
-//  const handleTagSelect = (tag: Tag) => {
-//  }
-
   useEffect (() => {
     const unsubscribe = WikiIdBus.subscribe (setWikiId)
     return () => unsubscribe ()
   }, [])
 
+  useEffect (() => {
+    setOpenItemIdx (menu.findIndex (item => (
+	location.pathname.startsWith (item.base || item.to))))
+  }, [location])
+
   useEffect (() => {
     if (!(wikiId))
       return
@@ -136,16 +87,18 @@ export default ({ user }: Props) => {
   return (
       <>
 	<nav className="px-3 flex justify-between items-center w-full min-h-[48px]
-			bg-yellow-50 dark:bg-red-975">
+			bg-yellow-200 dark:bg-red-975 md:bg-yellow-50">
 	  <div className="flex items-center gap-2 h-full">
-	    <Link to="/" className="mx-4 text-xl font-bold
-				    text-pink-600 hover:text-pink-400
-				    dark:text-pink-300 dark:hover:text-pink-100">
+	    <Link to="/"
+		  className="mx-4 text-xl font-bold text-pink-600 hover:text-pink-400
+			     dark:text-pink-300 dark:hover:text-pink-100">
 	      ぼざクリ タグ広場
 	    </Link>
-	    {menu.map (item => (
-		<Link to={item.to}
-		      className={cn ('h-full flex items-center',
+
+	    {menu.map ((item, i) => (
+		<Link key={i}
+		      to={item.to}
+		      className={cn ('hidden md:flex h-full items-center',
 				     (location.pathname.startsWith (item.base || item.to)
 				      ? 'bg-yellow-200 dark:bg-red-950 px-4 font-bold'
 				      : 'px-2'))}>
@@ -153,23 +106,83 @@ export default ({ user }: Props) => {
 		</Link>
 	    ))}
 	  </div>
+
 	  {user && (
-	      <div className="ml-auto pr-4">
+	      <div className="hidden md:block ml-auto pr-4">
 		<Link to="/users/settings"
 		      className="font-bold text-red-600 hover:text-red-400
 				 dark:text-yellow-400 dark:hover:text-yellow-200">
 		  {user.name || '名もなきニジラー'}
 		</Link>
 	      </div>)}
+
+	  <a href="#"
+	     className="md:hidden ml-auto pr-4
+			text-pink-600 hover:text-pink-400
+			dark:text-pink-300 dark:hover:text-pink-100"
+	     onClick={ev => {
+	       ev.preventDefault ()
+	       setMenuOpen (!(menuOpen))
+	     }}>
+	    {menuOpen ? '×' : 'Menu'}
+	  </a>
 	</nav>
-	<div className={cn ('bg-yellow-200 dark:bg-red-950',
-			    'text-white px-3 flex items-center w-full min-h-[40px]')}>
+
+	<div className="hidden md:flex bg-yellow-200 dark:bg-red-950
+			items-center w-full min-h-[40px]">
 	  {menu.find (item => location.pathname.startsWith (item.base || item.to))?.subMenu
 	   .filter (item => item.visible ?? true)
-	   .map (item => 'component' in item ? item.component : (
-	      <Link to={item.to} className="h-full flex items-center px-3">
+	   .map ((item, i) => 'component' in item ? item.component : (
+	      <Link key={i}
+		    to={item.to}
+		    className="h-full flex items-center px-3">
 		{item.name}
 	      </Link>))}
 	</div>
+
+	<div className={cn (menuOpen ? 'flex flex-col md:hidden' : 'hidden',
+			    'bg-yellow-200 dark:bg-red-975 items-start')}>
+	  <Separator />
+	  {menu.map ((item, i) => (
+	      <>
+		<a key={i}
+		   href="#"
+		   className={cn ('w-full min-h-[40px] flex items-center pl-8',
+				  i === openItemIdx && 'font-bold bg-yellow-50 dark:bg-red-950')}
+		   onClick={ev => {
+		     ev.preventDefault ()
+		     if (i === openItemIdx)
+		       {
+			 setMenuOpen (false)
+			 navigate (item.to)
+		       }
+		     else
+		       setOpenItemIdx (i)
+		   }}>
+		  {item.name}
+		</a>
+		{i === openItemIdx && (
+		    item.subMenu
+		    .filter (subItem => subItem.visible ?? true)
+		    .map ((subItem, j) => 'component' in subItem ? subItem.component : (
+			<Link key={j}
+			      to={subItem.to}
+			      className="w-full min-h-[36px] flex items-center pl-12
+					 bg-yellow-50 dark:bg-red-950">
+			  {subItem.name}
+			</Link>)))}
+	      </>))}
+	  {user && (
+	      <>
+		<Separator />
+		<Link to="/users/settings"
+		      className="w-full min-h-[40px] flex items-center pl-8
+				 font-bold text-red-600 hover:text-red-400
+				 dark:text-yellow-400 dark:hover:text-yellow-200">
+		  {user.name || '名もなきニジラー'}
+		</Link>
+	      </>)}
+	  <Separator />
+	</div>
       </>)
 }