To explore the Japanese legal system and treatment practices for people with mental disabilities who act in violation of the law, the project team formed a group to visit the medical institutions specified in the Act of Medical Observation in Japan from November 7 to 11, 2022. The purpose of the visit was to understand relevant treatment facilities and resource allocations in person, and listen to a wide variety of opinions, such as organizations of people with disabilities, government agencies, psychiatric institutions, and other experts and scholars. The visiting group comprehensively surveyed the actual conflicts and dilemmas in the Japanese system in terms of social defense and human rights protection. Both advantages and disadvantages were explored. These will be used as a reference for monitoring and adapting the implementation of the new treatment system in Taiwan.