PURPOSE: To obtain a correct distance between cars for controlling the same, by stopping the functions of alarming and controlling a distance between cars for a predetermined period of time from ON or OFF of a turn signal lamp switch, so as to maintain the velocity immediately before the turn signal lamp switch is turned ON by operating an accelerator, brake, clutch or the like.

CONSTITUTION: An image signal is taken out by an optical gauge for measuring a distance between cars 11, and is processed by a computer 5 to obtain the distance. The computer 5 receives, at this moment, car velocity information from the velocity sensor 2, brake information from the brake 3, clutch information from the clutch member 7 and turn signal information from the turn signal lamp switch 8 to effect required operations for actuating the control actuator 6 to control the car velocity. The situation at this moment is also transmitted to a driver through an alarm 9 or indicator 10 as visible or audible information. In such a manner, a correct distance between cars can be obtained also when the car is passing another car or changing a lane.