PURPOSE: To increase the braking effect of an armature by concentratedly flowing a current generated by back electromotive force due to the inertial rotation of said armature into a shunt coil without leaking it to the coil of a magnet switch.

CONSTITUTION: When a current is about to flow from a motor terminal 6 to a pull-in coil 3, a diode 5 which functions in the opposite direction prevents its flow, but, when starting, the diode functioning in the normal direction conducts a current from the pull-in coil 3 to the motor terminal 6. When a switch 2 is opened after operating a starter, an armature 9 continues to rotate by inertia, generating back electromotive force. A current generated by this back electromotive force flows from the armature 9, through a field coil 8, and to a shunt coil 10, which is turn, being excited by the back electromotive force, operates so as to brake the rotation of the armature 9. The back electromotive force which is about to flow to the pull-in coil 3 is prevented by the diode 5.