PURPOSE: To improve the smoothness of the operation for opening the door by detecting the release of engagement of a latch mechanism with a striker before starting to move the door, and starting a striker driving device in the door opening direction at the time of opening the door.

CONSTITUTION: In order to perfectly close a door 1, after a latch mechanism 4 and a striker 10 are engaged with each other, a striker driving device 8 is operated so as to move the striker 10 in the door 1 closing direction. At the time of opening the door, before starting to move the door 1, a detecting means detects release of the engagement of the latch mechanism 4 with the striker 10. Continuously, the striker driving device 8 is moved in the door opening direction in response to the signal from the detecting device. With this structure, before releasing the engagement of the latch mechanism 4 with the striker 10, the striker 10 is moved in the door opening direction, and the pushing reaction force of a weather strip 9 to the door 1 can be reduced.