PURPOSE: To maintain a distance sufficient to keep safety between one's car and the car ahead without giving a sense of incongruity to a driver by setting the target distance between the cars according to the car speed or the car speed and the traveling resistance while taking the distance between the two cars as reference when the distance keeping traveling is instructed.

CONSTITUTION: An instruction is given to a computer 15 through an instruction means when the distance from the car traveling ahead for which the driver thinks to be proper is obtained. Data such as the distance between two cars, car speed, relative speed, and engine output power or the like at the time when the instruction is given, are memorized. The traveling resistance is calculated from the car speed and the engine output power, the discrimination of uphills and downhills is performed, further the range of the proper distance between two adjacent cars is calculated by taking the car speed and the relative speed or the like into consideration. Whether or not the actual distance between the two cars is within the range of the proper distance is discriminated. When not, the proper deceleration speed is calculated to control actuators 7 and 8. Then, by taking this as reference, the target is set according to the car speed or the car speed and the traveling resistance.