Abstract: When information of a target, with which position information is associated, is extracted from map information, a relative position of a measurement subject, which is sensed by a radar, is obtained. Next, an absolute position of the measurement subject is estimated based on a current position of a vehicle, which is sensed through a GPS receiver, and a relative position of the measurement subject. When a distance between the measurement subject and the target is less than a predetermined threshold value, the measurement subject, which is sensed by the radar, is recognized as the target. An absolute position of the vehicle is computed based on the position information of the target and the relative position of the target. The position of the vehicle, which is sensed by the GPS receiver, is corrected to the computed absolute position.