To provide a device for preventing an accident caused by putting an open door or a crew who is going to get out of an automobile in contact with a vehicle coming closer from behind without the need for the crew, when getting out of the automobile, to identify the vehicle coming closer from behind.

An image processor 2 detects a movement vector from the image of the rear part of an automobile, photographed by a camera 1, to judge whether the vehicle coming closer from behind exists or not in accordance with a statistic in a screen. A door knob movement detecting part 3 detects the movement of a door knob when an occupant pulls the door knob to open the door. A door lock control part 5 locks the door not to be open when the vehicle coming closer from behind and the movement of the door knob are detected at the same time.