diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index 18270ce..60a4318 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -3,7 +3,7 @@ import toCamel from 'camelcase-keys'
 import { useState } from 'react'
 
 import PostFormTagsArea from '@/components/PostFormTagsArea'
-import DateTimeField from '@/components/common/DateTimeField'
+import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
 import Label from '@/components/common/Label'
 import { Button } from '@/components/ui/button'
 import { API_BASE_URL } from '@/config'
@@ -58,23 +58,11 @@ export default (({ post, onSave }: Props) => {
 	<PostFormTagsArea tags={tags} setTags={setTags}/>
 
 	{/* オリジナルの作成日時 */}
-	<div>
-	  <Label>オリジナルの作成日時</Label>
-	  <div className="my-1">
-	    <DateTimeField
-		className="mr-2"
-		value={originalCreatedFrom ?? undefined}
-		onChange={setOriginalCreatedFrom}/>
-	    以降
-	  </div>
-	  <div className="my-1">
-	    <DateTimeField
-		className="mr-2"
-		value={originalCreatedBefore ?? undefined}
-		onChange={setOriginalCreatedBefore}/>
-	    より前
-	  </div>
-	</div>
+	<PostOriginalCreatedTimeField
+	    originalCreatedFrom={originalCreatedFrom}
+	    setOriginalCreatedFrom={setOriginalCreatedFrom}
+	    originalCreatedBefore={originalCreatedBefore}
+	    setOriginalCreatedBefore={setOriginalCreatedBefore}/>
 
 	{/* 送信 */}
 	<Button onClick={handleSubmit}
diff --git a/frontend/src/components/PostOriginalCreatedTimeField.tsx b/frontend/src/components/PostOriginalCreatedTimeField.tsx
new file mode 100644
index 0000000..ffabc6b
--- /dev/null
+++ b/frontend/src/components/PostOriginalCreatedTimeField.tsx
@@ -0,0 +1,49 @@
+import DateTimeField from '@/components/common/DateTimeField'
+import Label from '@/components/common/Label'
+
+import type { FC } from 'react'
+
+type Props = {
+    originalCreatedFrom:      string | null
+    setOriginalCreatedFrom:   (x: string | null) => void
+    originalCreatedBefore:    string | null
+    setOriginalCreatedBefore: (x: string | null) => void }
+
+
+export default (({ originalCreatedFrom,
+		   setOriginalCreatedFrom,
+		   originalCreatedBefore,
+		   setOriginalCreatedBefore }: Props) => (
+    <div>
+      <Label>オリジナルの作成日時</Label>
+      <div className="my-1">
+	<DateTimeField
+	    className="mr-2"
+	    value={originalCreatedFrom ?? undefined}
+	    onChange={setOriginalCreatedFrom}
+	    onBlur={ev => {
+	      const v = ev.target.value
+	      if (!(v))
+		return
+	      const d = new Date (v)
+	      if (d.getSeconds () === 0)
+		{
+		  if (d.getMinutes () === 0 && d.getHours () === 0)
+		    d.setDate (d.getDate () + 1)
+		  else
+		    d.setMinutes (d.getMinutes () + 1)
+		}
+	      else
+		d.setSeconds (d.getSeconds () + 1)
+	      setOriginalCreatedBefore (d.toISOString ())
+	    }}/>
+	以降
+      </div>
+      <div className="my-1">
+	<DateTimeField
+	    className="mr-2"
+	    value={originalCreatedBefore ?? undefined}
+	    onChange={setOriginalCreatedBefore}/>
+	より前
+      </div>
+    </div>)) satisfies FC<Props>
diff --git a/frontend/src/components/common/DateTimeField.tsx b/frontend/src/components/common/DateTimeField.tsx
index c152f2a..5dbaae8 100644
--- a/frontend/src/components/common/DateTimeField.tsx
+++ b/frontend/src/components/common/DateTimeField.tsx
@@ -2,7 +2,7 @@ import { useEffect, useState } from 'react'
 
 import { cn } from '@/lib/utils'
 
-import type { FC } from 'react'
+import type { FC, FocusEvent } from 'react'
 
 
 const pad = (n: number) => n.toString ().padStart (2, '0')
@@ -22,10 +22,11 @@ const toDateTimeLocalValue = (d: Date) => {
 type Props = {
     value?:     string
     onChange?:  (isoUTC: string | null) => void
-    className?: string }
+    className?: string
+    onBlur?:    (ev: FocusEvent<HTMLInputElement>) => void }
 
 
-export default (({ value, onChange, className }: Props) => {
+export default (({ value, onChange, className, onBlur }: Props) => {
   const [local, setLocal] = useState ('')
 
   useEffect (() => {
@@ -42,5 +43,6 @@ export default (({ value, onChange, className }: Props) => {
 	    const v = ev.target.value
 	    setLocal (v)
 	    onChange?.(v ? (new Date (v)).toISOString () : null)
-	  }}/>)
+	  }}
+	  onBlur={onBlur}/>)
 }) satisfies FC<Props>
diff --git a/frontend/src/pages/posts/PostNewPage.tsx b/frontend/src/pages/posts/PostNewPage.tsx
index 102c9e4..f7ce25c 100644
--- a/frontend/src/pages/posts/PostNewPage.tsx
+++ b/frontend/src/pages/posts/PostNewPage.tsx
@@ -4,7 +4,7 @@ import { Helmet } from 'react-helmet-async'
 import { useNavigate } from 'react-router-dom'
 
 import PostFormTagsArea from '@/components/PostFormTagsArea'
-import DateTimeField from '@/components/common/DateTimeField'
+import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
 import Form from '@/components/common/Form'
 import Label from '@/components/common/Label'
 import PageTitle from '@/components/common/PageTitle'
@@ -189,23 +189,11 @@ export default (({ user }: Props) => {
 	  <PostFormTagsArea tags={tags} setTags={setTags}/>
 
 	  {/* オリジナルの作成日時 */}
-	  <div>
-	    <Label>オリジナルの作成日時</Label>
-	    <div className="my-1">
-	      <DateTimeField
-		  className="mr-2"
-		  value={originalCreatedFrom ?? undefined}
-		  onChange={setOriginalCreatedFrom}/>
-	      以降
-	    </div>
-	    <div className="my-1">
-	      <DateTimeField
-		  className="mr-2"
-		  value={originalCreatedBefore ?? undefined}
-		  onChange={setOriginalCreatedBefore}/>
-	      より前
-	    </div>
-	  </div>
+	  <PostOriginalCreatedTimeField
+	      originalCreatedFrom={originalCreatedFrom}
+	      setOriginalCreatedFrom={setOriginalCreatedFrom}
+	      originalCreatedBefore={originalCreatedBefore}
+	      setOriginalCreatedBefore={setOriginalCreatedBefore}/>
 
 	  {/* 送信 */}
 	  <Button onClick={handleSubmit}