The present invention is intended to, when rotation of a mirror rotation unit in a power-folding mirror is mechanically locked and its drive motor is thereby locked, make it possible to correctly detect this locked state. A motor 10 for a power-folding mirror is reversibly driven by an H-bridge drive circuit 12 formed of FETs 1 to 4. When the motor 10 is driven in normal rotation by turning the FETs 1 and 4 on and turning the FETs 2 and 3 off, the FET 1 is periodically turned off to detect a voltage of a terminal 10a of the motor 10 by means of a voltage detection circuit 14. When the FET 1 is turned off and the motor 10 is not locked, the motor 10 generates power by means of its inertial rotation, and when locked, the motor 10 generates no power, so the voltage detected by the voltage detection circuit 14 changes according to whether or not the motor 10 is locked. A CPU 20 determines whether or not the motor 10 is locked according to the voltage detected by the voltage detection circuit 14.