A lateral object that exists on a side of the vehicle is detected. When an estimated later-arriving lateral position reaches a predetermined threshold value under the condition in which the lateral object is detected, a lane change of the vehicle in a direction to a side of the lateral object is suppressed. When detecting that the vehicle moves laterally in a direction opposite to a side of a side vehicle, an avoidance flag is set to Fa=1. Subsequently, when the vehicle starts a lateral movement in a direction to the side of the side vehicle, a return flag is set to Fr=1. When the return flag is set to Fr=1 in this way, a suppression flag is set to F=0 until a setting time elapses, then the suppression of the lateral movement is forbidden.