The generator comprises a stator core 4 in which a three-phase stator coil 5 is wound and inserted into slots, a first rotor core 8 and a second rotor core 9 which are provided in the side of an inner diameter of this stator core 4 and rotate with a rotating shaft 7, a field coil 10 for magnetizing these first and second rotor cores 8 and 9 in different magnetic poles, and a plurality of magnetic poles 23 and 24 which are provided so as to extend to an axial direction of the rotating shaft 7 from the first and second rotor cores 8 and 9 and are arranged so as to have engagement alternately through predetermined gaps 25 and 26 between the magnetic poles and are opposite to the surface of the inner diameter of the stator core 4, and it is configured so that these magnetic poles 23 and 24 have a plurality of parts 23a, 24a and 23b, 24b in the axial direction and are stepwise formed and the respective parts are set to different widths in a rotational direction.