PURPOSE: To prevent a vehicle from quickly coming up close to a vehicle running ahead even if a follow-up running electronic control device fails.

CONSTITUTION: The upper limit value of a throttle opening signal 36 is computed based on the distance between our own vehicle and a vehicle running ahead, and the speed of our own vehicle. And when the throttle opening signal 36 equal to or more than the aforesaid upper limit value is sent out, it is judged that an electronic control device is abnormal, and an abnormality detecting electronic control device 16 is provided so as to direct our attention to the braking control of our own vehicle. And the abnormality detecting electronic control device 16 is also provided, which judges the abnormality of the vehicle with the actual throttle opening detected in place of the throttle opening signal 36.