PURPOSE: To improve the precision of the initial value of the estimated oil pressure by setting the first standard value and the second standard value which is higher than the first standard value in a brake operation oil pressure estimating means, and estimating the pressure reduction rate of the working oil pressure small, when the brake operation oil pressure in decompression which is estimated from the opening/closing valve time is lower than the second standard value.

CONSTITUTION: A slip control means 70 for controlling the electromagnetic type opening/closing valve 36A or 37A for brake operation for the left and right rear wheels and the electromagnetic type opening/closing valve 36B or 37B for relief is equipped with a brake oil pressure estimating means. Each time (opening/closing valve time) in the pressure increase and decrease of the brake oil pressure by the electromagnetic opening/closing valve is detected, and the brake oil pressure is estimated and calculated on the basis of the accumulated value of the additional values and reduction valuees. In this case, the first standad valve P1 on the low pressure side and the second standard value P2 on the high pressure side are set, and if the estimated brake oil pressure P is lower than the second standard value P2, the reduction rate of the brake oil pressure for the pressure reduction time is made gentle in comparison with the case where the estimated brake oil pressure P is higher than the second standard value P2.