diff --git a/update_db.py b/update_db.py
index 62f2dbe..036f12f 100644
--- a/update_db.py
+++ b/update_db.py
@@ -18,7 +18,7 @@ import requests
 
 # TODO: “何もしなぃ” を意味する None と区別可能にするため，NULL クラスを別途用意すること
 DbNull = None
-DbNullType = None
+DbNullType = type (None)
 
 
 class VideoSearchParam (TypedDict):
@@ -33,7 +33,7 @@ class VideoSearchParam (TypedDict):
 class VideoResult (TypedDict):
     contentId:      str
     title:          str
-    tags:           list[str]
+    tags:           str
     description:    str
     viewCounter:    int
     startTime:      str
@@ -91,6 +91,7 @@ def update_tables (
 ) -> None:
     video_ids: list[int] = []
     for datum in api_data:
+        tag_names = datum['tags'].split ()
         video = VideoDto (code          = datum['contentId'],
                           title         = datum['title'],
                           description   = datum['description'],
@@ -107,12 +108,12 @@ def update_tables (
             for vt in video_tags:
                 tag = tag_dao.find (vt.tag_id)
                 if (tag is not None
-                        and (tag.name not in datum['tags'])
+                        and (tag.name not in tag_names)
                         and (tag.id_ is not None)):
                     tag_ids.append (tag.id_)
             video_tag_dao.untag_all (video.id_, tag_ids, now)
         tags: list[TagDto] = []
-        for tag_name in datum['tags']:
+        for tag_name in tag_names:
             tag = tag_dao.fetch_by_name (tag_name)
             if tag is None:
                 tag = TagDto (name = tag_name)
@@ -139,12 +140,12 @@ def update_tables (
                                       vpos_ms       = com['vposMs'])
                 comment_dao.upsert (comment, False)
 
-    alive_video_ids = [d['contentId'] for d in api_data]
+    alive_video_codes = [d['contentId'] for d in api_data]
 
     lost_video_ids: list[int] = []
     videos = video_dao.fetch_alive ()
     for video in videos:
-        if video.id_ is not None and video.id_ not in alive_video_ids:
+        if video.id_ is not None and video.code not in alive_video_codes:
             lost_video_ids.append (video.id_)
 
     video_dao.delete (lost_video_ids, now)
@@ -573,7 +574,7 @@ class VideoTagDao:
             self,
             video_id:   int,
             tag_ids:    list[int],
-            now:        datetime
+            now:        datetime,
     ) -> None:
         if not tag_ids:
             return