Provided is a compound motor (14) comprising a magnet rotor (19) supported by bearings (B3, B4) in a rotatable manner, a winding rotor (20) supported by bearings (B5, B6) in a rotatable manner relative to the magnet rotor (19) at the inner side of the magnet rotor (19) and having rotor winding units (20b), and slip ring mechanisms (25). A space is formed in the inner circumference of the winding rotor (20). At least a part of the slip ring mechanisms (25) is arranged in the space of the inner circumference of the winding rotor (20). The bearings (B3 to B6) include bearings (B3, B6), the internal diameter of each is larger than the size of slip ring mechanisms (25) with respect to the radial direction. The bearings (B3, B6) are arranged outside the slip ring mechanisms (25) with respect to the radial direction.