To prevent a driving member from obstructing the motion of a lock mechanism and improve the convenience by turning a reverse rotating relay switch ON for a prescribed time when a normal rotating relay switch is OFF.

A driving member 5 is driven from an initial position to a lock end position, whereby the latch 4b of a lock mechanism 4 is moved from a half lock position to a full lock position. The driving member 5 is driven by a motor 3, and the drive of the motor 3 is controlled by a drive control circuit 1. When a normal rotating relay switch 12 is ON by a charging circuit 14, charging is performed, and when it is OFF thereafter, a reverse rotating relay switch 13 is ON for a prescribed time by the discharge of the charged electric charge. Therefore, even when a neutral switch 23 fails, the motor 3 is necessarily reversely rotated after normal rotation, and the driving member 5 thus never obstructs the motion of the lock mechanism 4.