PURPOSE: To prevent the abrasion and welding of a contact by the operation of a relay with the simple structure in spite of the condition that a motor is connected to a power source for driving even in the case where the relay is switched to the grounding side so as to separate the motor from the power source after the motor is stopped by an external force or the like.

CONSTITUTION: A motor 5, in which one of a first and a second terminals 5a, 5b is connected to a power source 7 and the other is grounded, is stopped by a first relay 9, which is connected to the first terminal 5a of the motor 5, and a second relay 11, which is connected to the second terminal 5b of the motor 5. The first and the second terminals 5a, 5b are connected to the power source 7 together by the first and the second relays 9, 11, and next, the first and the second terminals 5a, 5b are grounded by the first and the second relays 9, 11 at the same time.