Imperial Household Law main subject Imperial House of Japan
The Imperial Household Law of 1947 (皇室典範, Kōshitsu Tenpan) is a Japanese law that governs the line of imperial succession, the membership of the imperial family, and several other matters pertaining to the administration of the Imperial Household.  
In 2017, the National Diet changed the law to enable the Emperor to abdicate within three years. With this change, Emperor Akihito abdicated on 30 April 2019.Passage of the law
The Imperial Household Law was passed during the Shōwa era on January 16, 1947, by the last session of the Imperial Diet. This law superseded the Imperial Household Law of 1889, which had enjoyed co-equal status with the Constitution of the Empire of Japan and could only be amended by the Emperor. The revised statute is subordinate to the Constitution of Japan, which went into effect on May 3, 1947. It develops Chapter 1: Article 2 of the Constitution of Japan, which states: "The Imperial Throne shall be dynastic and succeeded to in accordance with the Imperial House Law passed by the Diet".The chapters of the Imperial Household Law addresses the following: