PURPOSE: To miniaturize and lighten the device by controlling each field circuit by two pairs of bridge circuits sharing two of six field choppers while controlling two pairs of armature circuits by one armature chopper.

CONSTITUTION: The field choppers 24, 25 in the field choppers 15W18, 24, 25 are shaped, a first bridge is constituted by the field choppers 15, 16, 24, 25 and controls the currents of field winding 19, and a second bridge is constituted by the field choppers 17, 18, 24, 25 and controls the currents of field winding 20. The currents of armatures 7, 8 are controlled by the armature chopper 21. Accordingly, the controller can be miniaturized and lightened because the armature circuits corresponding to two circuits can be controlled by one armature chopper.