In a rotation apparatus including a motor and a speed reducer, the speed reducer includes a casing, an internal gear integrated with the casing, a planetary gear internally engaged with the internal gear, and a carrier body arranged in an axial side portion of the planetary gear, the motor and the speed reducer are connected with each other via an adapter, the adapter includes a motor-fixed surface fixed to the motor, a carrier-fixed surface fixed to the carrier body, and an externally fixed surface that is not parallel with the carrier-fixed surface and is fixed to an external member, a driven member is connected to the casing, the driven member, the speed reducer, and the externally fixed surface are overlapped with each other when viewed from a radial direction, and the driven member is rotated within a range of 180 degrees.