Bikkaiho (Adultery Control Law) (密懐法)
Bikkaiho (Adultery Control Law) was a law that stipulated the handling of adultery. It originated from Bukeho (the law system for the samurai society and military government). It is equivalent to the adultery law after the Meiji era.
In the medieval times, there was a discrepancy between written code and common law. In the former, the article 34 of Goseibai-shikimoku (code for conduct for samurai) stated 'Regardless of rape or adultery, an adulterer shall forfeit a half of his shoryo (territory) and be banned from entering government service. If he does not own shoryo (territory), he shall be subject to Onru (exile to the farthest distant island).
Same punishment applies to an adulteress.'
However, in the latter, megataki uchi (revenge on the adulterer) was practiced, in which a husband killed the adulterer as 'sukuse no teki' (fateful enemy). But when megataki uchi was practiced, sometimes the husband was punished for the crime of murder because it was impossible for the husband to produce evidence by having the adulterer confess because he had killed the adulterer.
Meanwhile, the Muromachi bakufu made a landmark ruling in some respects in 1479. The bakufu set a legal precedent that if the real husband killed his wife first for the reason of adultery, the adulterer who had brought about the cause would be considered as megataki (adulterer), and for this reason, even if the husband practiced megataki uchi (revenge oneself on the adulterer), it would not constitute a crime of murder, and thus, the husband was innocent. This ruling backed by the concept of approving 'murder of adulterer and adulteress' based on common law was welcomed by Sengoku daimyo (Japanese territorial lord in the Sengoku period) and was introduced in one bunkokuho (the law individual Sengoku-daimyo enforced in their own domain) after another. Jinkaishu (bunkokuho enforced by Tanemune DATE) and Rokkakushi shikimoku (bunkokuho of the Rokkaku clan) prescribed murder of the adulteress (however, if the adulterer was murdered in the bedroom, it was not required to murder the adulteress), and in an extreme case of Chosokabe Motochika Hyakkajo (bunkokuho by the Chosokabe clan) prescribed that if the husband didn't murder the adulteress, the adulterer, the adulteress and the husband would all be sentenced to death.
The Edo bakufu disapproved self-help on one hand, but on the other hand, from the standpoint of enforcing the ethics of samurai families, it excluded Katakiuchi (revenge) and megataki uchi (revenge on the adulterer). Furthermore, when a daughter committed adultery, it constituted a violation of parental authority, and her father was allowed to murder her (yet, megataki uchi by a commoner was severely punished as he was deemed one who does not know his place, although megataki uchi by samurai was tolerated). However, when megataki uchi (revenge oneself on the adulterer) was practiced, the fact that his wife had been unfaithful was exposed to the outside world, and some people thought that it only made a samurai lose face. Consequently, in many case, they saved the situation among themselves by collecting reparations known as 'maotoko seven ryo two bu' (compensation seven ryo two bu for adultery) from the adulterer, or divorcing the adulteress.