A double-stator includes outer and inner stators each having magnetic poles. Outer-stator and inner-stator windings are connected in series in phases, thereby generating winding magnetomotive force. Outer magnets and inner magnets of a rotor are arranged in a rotor core in the circumferential direction, the outer and inner magnets being alternated between a radially outward portion and a radially inward portion, at a pitch equal to that of the poles of the outer and inner stators so as to be magnetized so that a radially outer side thereof will serve as N poles or S poles and that a radially inner side thereof will serve as S poles or N poles. The rotor core includes outer poles formed between the outer magnets circumferentially adjacent to each other in the radially outward portion, and inner poles formed between the inner magnets circumferentially adjacent to each other in the radially inward portion.