Abstract: A slip factor and a wheel acceleration are respectively calculated on the basis of a wheel speed; an increase/decrease pressure quantity for the brake pressure is calculated in an increase/decrease pressure quantity calculating means on the basis of the slip factor and the wheel acceleration; the wheel acceleration is subjected to waveform-shaping with a predetermined hysteresis characteristic to form pulses; the period of the pulses are calculated by a period calculating means; the increase/decrease pressure quantity calculated by the increase/decrease pressure quantity calculating means is corrected by an increase/decrease pressure quantity correcting means in response to the period; the output of the increase/decrease pressure quantity correcting means is received by a bad road judging means in which judgment is made as to whether the road is bad or not, and a correction quantity of the increase/decrease pressure quantity correcting means is changed by a correction changing means.