An AC motor-generator includes a rotor made up of a first inductor core and a second inductor core arrayed in an axial direction of a rotary shaft. A plurality of permanent magnets are arrayed at an interval of 2&pgr; in electrical angle of an armature away from each other in the periphery of each of the first and second inductor cores. Each permanent magnet is magnetized in a radius direction of the first and second inductor cores so as to be opposed to a magnetomotive force produced by a field winding, thereby resulting in quick disappearance of the magnetic flux of the field upon disappearance of the magnetomotive force from the field winding.