To actively control and to comfortably brake by allowing a down slope speed to depend on a position of a throttle valve and a change gear speed where a low-speed range traveling speed is just put in.

A function 'controlled mountain descending' is inputted automatically by an electronic device 9 or by a driver via a switch 11. Then, the driver takes the foot off a brake pedal or an accelerator pedal. Immediately after acting the down control, an ASR(drive slip regulator) 5' is excited so that the brake pressure is directly introduced to a brake cylinder 7 of a wheel of a front axle 1 (active brake). In this case, the electronic device 9 controls the speed of a vehicle to the preset speed and hold it irrelevant to the inclination by an appropriate control of a solenoid valve 8. When the traveling speed is increased during the down slope operation, the preset down slope speed of the vehicle is increased from the lowest speed to a speed dependent on the throttle valve position and the down slope speed without/with operating the accelerator pedal is dependent on the put-in change gear speed.