受到家臣錦織剛清指控中村藩主相馬誠胤被其家屬不當監禁於精神病院的複雜法律事件「相馬事件」影響，催生了1900 年日本頒佈「精神病者監護法」，該法要求病人家屬善盡照顧責任，並使日本在之後50 年持續實行私宅監置制度。「精神衛生法」在二戰結束後聯軍佔領時期的1950 年頒佈，該法禁止私宅監置、鼓勵建置精神病院，而造成1960 年後私人精神病院太多。1964 年一名思覺失調症病人攻擊美國駐日本大使，進一步強化了以醫院為中心的精神醫療系統，使得1968 年世界衛生組織顧問以社區為本的精神醫療的建議，也被擱置，直至因一名精神病人在住院期間被虐待致死的「宇都宮病院事件」轟動國際，且國際專家到日訪問後，日本政府才對原來的「精神衛生法」做了重大修訂，且在1987 年頒佈「精神保健法」，開始促進以社區為本的精神醫療，並保障住院病人的人權。1995 年「精神保健法」再被修訂成「精神保健福祉法」，以將社會福利服務納入法條。在「池田小學校事件」發生兩年後的2003 年，日本頒佈「醫療觀察法」以治療及照顧那些犯了嚴重罪刑的精神病人。

After the Meiji Revolution in 1867, Japan adopted Western medicine and hospital system. Japan enacted the first mental health legislation “the Home Custody Act of Mental Patients” in 1900. The complicated legal and forensic “the Soma event” triggered the enactment of this legislature. The law was public security-oriented to hide vagrancy of mental patients. Family was made responsible for the care of a member who became mentally sick. The law enabled the home custody of mental patients for half a century. “The Mental Hygiene Law“ was enacted in 1950 after World War II under the occupation of Allied Forces. The law prohibited the home custody and promoted the building of psychiatric hospitals. This policy resulted in the mushrooming of private psychiatric hospitals from 1960’s. This hospital-centered mental health system was strengthened after an attack by a schizophrenic patient to an American ambassador to Japan in 1964. Recommendations by World Health Organization consultants to promote community-based psychiatry in 1968 were just ignored. The tide changed when a scandal of private mental hospital (the Utsunomiya Hospital event) became known to international organizations. After the visit of International Jurist Organization and World Psychiatric Organization, Japanese government made a major revision in the Mental Hygiene Law. This amendment resulted in the enactment of the 1987 “Mental Health Law,” to promote community-based psychiatry and to protect the human rights of inpatients. In 1995, the Mental Health Law was further amended to “Mental Health and Welfare Law” to include social and welfare services. After Ikeda Primary School event, the Medical Treatment and Supervision Act was enacted in 2003 to treat and care mental patients who committed serious crimes. The overview of mental health legislation shows the important rôle played by social events and scandals to shape mental health laws in Japan.