An assembly device includes a shaft assembly having a plurality of pistons installed on an outer peripheral portion of a swash plate via shoes. The assembly device has a shaft support portion which supports a shaft having the swash plate in a vertical axis posture, a guide member, a shoe incorporation mechanism, a carriage which conveys the plurality of pistons in the vertical axis posture, and a piston holding portion which holds the plurality of pistons. The guide member is equipped with a first guide surface and a second guide surface.