A collision avoidance ECU estimates a traveling locus based on an estimated curve radius of an own vehicle in a basic traveling locus estimating unit, and in a changed traveling locus estimating unit, obtains separation distances between an own vehicle and white lines based on the relative positional relationship between an own vehicle and the white lines, and estimates, as a changed traveling locus, a route along the white lines with the obtained separation distances maintained. In a collision judging unit, when auto-steering control and departure warning control are not performed, collision judgment is performed based on the basic traveling locus estimated in the basic traveling locus estimating unit, and when the auto-steering control and departure warning control are performed, the traveling locus is changed to the changed traveling locus estimated in the changed traveling locus estimating unit and collision judgment is performed.