Information for generating a target speed pattern is computed from information acquired from various sensors and a running mode input switch, so as to generate the target speed pattern (S16). A process for determining whether to form a vehicle group or not calculates the difference between the target vehicle pattern of the own vehicle and a target speed pattern of another vehicle or vehicle group obtained through inter-vehicle communication, so as to determine whether to form the vehicle group or not (S22, S28, S32). This can determine whether to run solo or form a vehicle group according to a driver's demand.