A cruise control capable of maintaining the speed of a vehicle at a set cruise speed is selected when the headway distance to a preceding vehicle is equal to or greater than a set distance. Headway distance control, maintaining the headway distance to the preceding vehicle at a required value, is selected when the headway distance is smaller than a set distance. Fleet driving, in which the vehicle runs at the same set speed as that of the preceding vehicle, is enabled by increasing the vehicle speed upper limit existing under the headway distance control above a set cruise speed.