This system was established on October 14, 826 based on sojo (report to the Emperor) made by KIYOHARA no Natsuno ("Ruiju Sandaikyaku": Shinno-ningoku Daijokanpu (the official document issued by Daijokan, Grand Council of the state)).
天長3年9月6日(旧暦)（826年10月10日）、清原夏野の奏上に基づき制定された（『類聚三代格』：親王任国太政官符）。