PURPOSE: To improve detection accuracy by measuring each speed pulse of right and left wheels at a same time by separate counters and detecting the wheel revolution difference according to the measurement difference between both counters.

CONSTITUTION: Wheel speed sensors 10 and 20 detect the speed of the right and left driving wheels respectively, and the signals thus obtained are counted by a counter 80 and a latch circuit 90, passing through wave-form shaping circuits 30 and 40 and gate circuits 60 and 70. A logic circuit 110 controls the counted number. A subtraction circuit 100 performs the reduction of the counted value latched by the right and left counters 80 and 90, and the difference is output into a comparison circuit 120, which compares the difference with the signal from a comparison value setting circuit 130, and operates according to the result, right and left brake actuators through amplifiers 140 and 150, in order to prevent the wheel revolution difference from exceeding a limit. As a digital subtraction device is used, the detection of the wheel revolution difference which is hardly influenced by noise in comparison to the conventional analogue comparison device can be obtained.