A medical apparatus remanufacturing method includes: disassembling a housing including a first housing and a second housing. The first housing can include a boss that is press-fitted to a boss hole of a press-fitted portion of a second housing to form an assembled state in which the first housing and the second housing are assembled to each other. The housing is disassembled by changing a temperature of at least one of the boss or the press-fitted portion to decrease a contact surface pressure between the boss and the boss hole, and removing the boss from the boss hole to release the assembled state.