PROBLEM TO BE SOLVED: To exactly determine whether passing control should be continued or interrupted from a relationship between a preceding vehicle and an own vehicle in the case that the preceding vehicle tries to move to a branch lane from a main lane when the own vehicle passes the preceding vehicle (or during the passing).SOLUTION: When an own vehicle A passes a preceding vehicle B, a drive support control unit 11 examines whether or not a left turn signal lamp of the preceding vehicle B is lit (S31) on the basis of an image from an on-vehicle camera 22, compares a standby determination threshold T4' which higher than an interruption determination threshold T4 and a preceding vehicle lateral position L4 (S34) when it is determined that the left turn signal lamp is lit, sets an interruption determination flag F (F←1,S37) since a possibility that the preceding vehicle moves to a branch lane is high when the preceding vehicle lateral position L4 is smaller than the standby determination threshold T4' (T4