Vehicular air conditioner compressor

The present invention provides a rotating apparatus. The rotating apparatus includes a rotor (83) and a motor generator (MG). The rotor (83) includes a belt holder (83a) on its outer circumferential surface. The belt holder (83a) transmits power between an engine (E) and the rotor (83). The motor generator (MG) is accommodated in and operably connected to the rotor (83). The motor generator (MG) selectively functions as at least one of a motor and a generator. The motor generator (MG) is arranged inside the belt holder (83a) such that the motor generator (MG) is surrounded by the belt holder (83a).