From the end of the Heian period, the Hirata family served as secretary 'suino' at the Bureau of Archives for generations; the successive heads of the family recorded things including knowledge necessary for political affairs, public affairs, and ceremonies in a diary to hand down to their descendants.
平田家は平安時代末期より代々蔵人所出納を務め、後には世襲してきたが、政務や公事、儀式に必要な知識などを歴代当主が日記の形式で書き残して子孫へと伝えていった。