diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index e40c09e..a254ce1 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -2,7 +2,8 @@ import axios from 'axios'
 import toCamel from 'camelcase-keys'
 import { useState } from 'react'
 
-import TextArea from '@/components/common/TextArea'
+import PostFormTagsArea from '@/components/PostFormTagsArea'
+import Label from '@/components/common/Label'
 import { Button } from '@/components/ui/button'
 import { API_BASE_URL } from '@/config'
 
@@ -24,7 +25,7 @@ export default (({ post, onSave }: Props) => {
   const handleSubmit = async () => {
     const res = await axios.put (`${ API_BASE_URL }/posts/${ post.id }`, { title, tags },
 	{ headers: { 'Content-Type':     'multipart/form-data',
-		     'X-Transfer-Code':  localStorage.getItem ('user_code') || '' } } )
+		     'X-Transfer-Code':  localStorage.getItem ('user_code') ?? '' } } )
     const data = toCamel (res.data as any, { deep: true }) as Post
     onSave ({ ...post,
 	      title:  data.title,
@@ -35,9 +36,7 @@ export default (({ post, onSave }: Props) => {
       <div className="max-w-xl pt-2 space-y-4">
 	{/* タイトル */}
 	<div>
-	  <div className="flex gap-2 mb-1">
-	    <label className="flex-1 block font-semibold">タイトル</label>
-	  </div>
+	  <Label>タイトル</Label>
 	  <input type="text"
 		 className="w-full border rounded p-2"
 		 value={title}
@@ -45,11 +44,7 @@ export default (({ post, onSave }: Props) => {
 	</div>
 
 	{/* タグ */}
-	<div>
-	  <label className="block font-semibold">タグ</label>
-	  <TextArea value={tags}
-		    onChange={ev => setTags (ev.target.value)}/>
-	</div>
+	<PostFormTagsArea tags={tags} setTags={setTags}/>
 
 	{/* 送信 */}
 	<Button onClick={handleSubmit}
diff --git a/frontend/src/components/PostFormTagsArea.tsx b/frontend/src/components/PostFormTagsArea.tsx
new file mode 100644
index 0000000..38ffd70
--- /dev/null
+++ b/frontend/src/components/PostFormTagsArea.tsx
@@ -0,0 +1,84 @@
+import axios from 'axios'
+import toCamel from 'camelcase-keys'
+import { useRef, useState } from 'react'
+
+import TagSearchBox from '@/components/TagSearchBox'
+import Label from '@/components/common/Label'
+import TextArea from '@/components/common/TextArea'
+import { API_BASE_URL } from '@/config'
+
+import type { FC, SyntheticEvent } from 'react'
+
+import type { Tag } from '@/types'
+
+const SEP = /\s/
+
+
+const getTokenAt = (value: string, pos: number) => {
+  let start = pos
+  while (start > 0 && !(SEP.test (value[start - 1])))
+    --start
+
+  let end = pos
+  while (end < value.length && !(SEP.test (value[end])))
+    ++end
+
+  return { start, end, token: value.slice (start, end) }
+}
+
+
+const replaceToken = (value: string, start: number, end: number, text: string) => (
+    `${ value.slice (0, start) }${ text }${ value.slice (end) }`)
+
+
+type Props = {
+    tags:     string
+    setTags:  (tags: string) => void }
+
+
+export default (({ tags, setTags }: Props) => {
+  const ref = useRef<HTMLTextAreaElement> (null)
+
+  const [bounds, setBounds] = useState<{ start: number; end: number }> ({ start: 0, end: 0 })
+  const [suggestions, setSuggestions] = useState<Tag[]> ([])
+  const [suggestionsVsbl, setSuggestionsVsbl] = useState (false)
+
+  const handleTagSelect = (tag: Tag) => {
+    setSuggestionsVsbl (false)
+    const textarea = ref.current!
+    const newValue = replaceToken (tags, bounds.start, bounds.end, tag.name)
+    setTags (newValue)
+    requestAnimationFrame (async () => {
+      const p = bounds.start + tag.name.length
+      textarea.selectionStart = textarea.selectionEnd = p
+      textarea.focus ()
+      await recompute (p, newValue)
+    })
+  }
+
+  const recompute = async (pos: number, v: string = tags) => {
+    const { start, end, token } = getTokenAt (v, pos)
+    setBounds ({ start, end })
+    const res = await axios.get (`${ API_BASE_URL }/tags/autocomplete`, { params: { q: token } })
+    setSuggestions (toCamel (res.data as any, { deep: true }) as Tag[])
+    setSuggestionsVsbl (suggestions.length > 0)
+  }
+
+  return (
+      <div>
+	<Label>タグ</Label>
+	<TextArea
+	    ref={ref}
+	    value={tags}
+	    onChange={ev => setTags (ev.target.value)}
+	    onSelect={async (ev: SyntheticEvent<HTMLTextAreaElement>) => {
+	      const pos = (ev.target as HTMLTextAreaElement).selectionStart
+	      await recompute (pos)
+	    }}/>
+	<TagSearchBox suggestions={suggestionsVsbl && suggestions.length
+				   ? suggestions
+				   : [] as Tag[]}
+		      activeIndex={-1}
+		      onSelect={handleTagSelect}/>
+      </div>)
+}) satisfies FC<Props>
diff --git a/frontend/src/components/TagSearch.tsx b/frontend/src/components/TagSearch.tsx
index fc5723f..55ac949 100644
--- a/frontend/src/components/TagSearch.tsx
+++ b/frontend/src/components/TagSearch.tsx
@@ -15,9 +15,9 @@ export default (() => {
   const location = useLocation ()
   const navigate = useNavigate ()
 
+  const [activeIndex, setActiveIndex] = useState (-1)
   const [search, setSearch] = useState ('')
   const [suggestions, setSuggestions] = useState<Tag[]> ([])
-  const [activeIndex, setActiveIndex] = useState (-1)
   const [suggestionsVsbl, setSuggestionsVsbl] = useState (false)
 
   const whenChanged = async (ev: React.ChangeEvent<HTMLInputElement>) => {
@@ -33,7 +33,7 @@ export default (() => {
     const res = await axios.get (`${ API_BASE_URL }/tags/autocomplete`, { params: { q } })
     const data = res.data as Tag[]
     setSuggestions (data)
-    if (suggestions.length)
+    if (suggestions.length > 0)
       setSuggestionsVsbl (true)
   }
 
diff --git a/frontend/src/components/TagSearchBox.tsx b/frontend/src/components/TagSearchBox.tsx
index 2a40b5f..79c912f 100644
--- a/frontend/src/components/TagSearchBox.tsx
+++ b/frontend/src/components/TagSearchBox.tsx
@@ -10,7 +10,7 @@ type Props = { suggestions: Tag[]
 
 
 export default (({ suggestions, activeIndex, onSelect }: Props) => {
-  if (!(suggestions.length))
+  if (suggestions.length === 0)
     return
 
   return (
@@ -21,8 +21,7 @@ export default (({ suggestions, activeIndex, onSelect }: Props) => {
 	    <li key={tag.id}
 		className={cn ('px-3 py-2 cursor-pointer hover:bg-gray-300 dark:hover:bg-gray-700', 
 			       i === activeIndex && 'bg-gray-300 dark:bg-gray-700')}
-		onMouseDown={() => onSelect (tag)}
-	    >
+		onMouseDown={() => onSelect (tag)}>
 	      {tag.name}
 	      {<span className="ml-2 text-sm text-gray-400">{tag.postCount}</span>}
 	    </li>))}
diff --git a/frontend/src/components/common/TextArea.tsx b/frontend/src/components/common/TextArea.tsx
index 951dab2..64178da 100644
--- a/frontend/src/components/common/TextArea.tsx
+++ b/frontend/src/components/common/TextArea.tsx
@@ -1,10 +1,9 @@
-import React from 'react'
+import { forwardRef } from 'react'
 
-type Props = { value?:    string
-	       onChange?: (event: React.ChangeEvent<HTMLTextAreaElement>) => void }
+import type { TextareaHTMLAttributes } from 'react'
 
+type Props = TextareaHTMLAttributes<HTMLTextAreaElement>
 
-export default ({ value, onChange }: Props) => (
-    <textarea className="rounded border w-full p-2 h-32"
-	      value={value}
-	      onChange={onChange}/>)
+
+export default forwardRef<HTMLTextAreaElement, Props> (({ ...props }, ref) => (
+    <textarea ref={ref} className="rounded border w-full p-2 h-32" {...props}/>))
diff --git a/frontend/src/pages/posts/PostListPage.tsx b/frontend/src/pages/posts/PostListPage.tsx
index c3a4929..fdda686 100644
--- a/frontend/src/pages/posts/PostListPage.tsx
+++ b/frontend/src/pages/posts/PostListPage.tsx
@@ -127,7 +127,7 @@ export default () => {
 		  }}/>)
 	       : !(loading) && '広場には何もありませんよ．'}
 	      {loading && 'Loading...'}
-	      <div ref={loaderRef} className="h-12"></div>
+	      <div ref={loaderRef} className="h-12"/>
 	    </Tab>
 	    {tags.length === 1 && (
 		<Tab name="Wiki">
diff --git a/frontend/src/pages/posts/PostNewPage.tsx b/frontend/src/pages/posts/PostNewPage.tsx
index 5465aab..97e9425 100644
--- a/frontend/src/pages/posts/PostNewPage.tsx
+++ b/frontend/src/pages/posts/PostNewPage.tsx
@@ -3,22 +3,24 @@ import { useEffect, useState, useRef } from 'react'
 import { Helmet } from 'react-helmet-async'
 import { useNavigate } from 'react-router-dom'
 
+import PostFormTagsArea from '@/components/PostFormTagsArea'
 import Form from '@/components/common/Form'
 import Label from '@/components/common/Label'
 import PageTitle from '@/components/common/PageTitle'
-import TextArea from '@/components/common/TextArea'
 import MainArea from '@/components/layout/MainArea'
 import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { API_BASE_URL, SITE_TITLE } from '@/config'
 import Forbidden from '@/pages/Forbidden'
 
+import type { FC } from 'react'
+
 import type { User } from '@/types'
 
 type Props = { user: User | null }
 
 
-export default ({ user }: Props) => {
+export default (({ user }: Props) => {
   if (!(['admin', 'member'].some (r => user?.role === r)))
     return <Forbidden/>
 
@@ -131,7 +133,7 @@ export default ({ user }: Props) => {
 	  {/* タイトル */}
 	  <div>
 	    <Label checkBox={{
-		label:	  '自動',
+		label:    '自動',
 		checked:  titleAutoFlg,
 		onChange: ev => setTitleAutoFlg (ev.target.checked)}}>
 	      タイトル
@@ -147,7 +149,7 @@ export default ({ user }: Props) => {
 	  {/* サムネール */}
 	  <div>
 	    <Label checkBox={{
-		label:	  '自動',
+		label:    '自動',
 		checked:  thumbnailAutoFlg,
 		onChange: ev => setThumbnailAutoFlg (ev.target.checked)}}>
 	      サムネール
@@ -177,12 +179,7 @@ export default ({ user }: Props) => {
 	  </div>
 
 	  {/* タグ */}
-	  {/* TextArea で自由形式にする */}
-	  <div>
-	    <Label>タグ</Label>
-	    <TextArea value={tags}
-		      onChange={ev => setTags (ev.target.value)}/>
-	  </div>
+	  <PostFormTagsArea tags={tags} setTags={setTags}/>
 
 	  {/* 送信 */}
 	  <Button onClick={handleSubmit}
@@ -192,4 +189,4 @@ export default ({ user }: Props) => {
 	  </Button>
 	</Form>
       </MainArea>)
-}
+}) satisfies FC<Props>