To specify an object to be controlled by detecting a vehicle position according to regrouped signals based on a past dealing width, if a past width change amount to be of target reflection signals is larger than a predetermined amount and no crack exists in a peak shape.

The signal processor 3 comprises a radar signal processing unit 12, and an object-to-be-controlled recognition unit 13. The unit 12 judges whether a change amount of a past dealing width of reflection signals from a radar antenna 1 is larger than a predetermined amount or not, and judges whether a crack exists in a peak shape of a received signal or not in the case of large change amount. If no crack exists, the unit 12 regroups based on the paste dealing width, individually stores the received signal based on the width and a signal having no past dealing, and detects a position of the target based on the stored signal data. The unit 13 judges whether the detected target is within an own lane or not. The judgment of whether the detected target is within the lane or not is decided according to number of times of detections at a bean of a specific angle of the radar.