PURPOSE: To efficiently stop a vehicle and prevent a vehicle accident by automatically turning an auxiliary brake off when a driving wheel lock is judged to occur, making various situation estimations in each prescribed time, and automatically turning the auxiliary brake on.

CONSTITUTION: The first and second threshold value setting means 1, 2 for detecting the slips of the driving wheels of a vehicle are provided, and the minimum driving wheel speed detected by a driving wheel speed detecting means 3 is compared 4 with the first threshold value. A judging means 5 judging whether one of the ABS, ASR, and brake of the vehicle is operated or not is provided. When the judgment is no and the minimum driving wheel speed is the first threshold value or below, an auxiliary brake is turned off by the first control means 6. The driving wheel speed is compared 10 with the first threshold value. When the driving wheel speed is recovered to the first threshold value within the prescribed time after the auxiliary brake is turned off, the auxiliary brake is turned on.