PURPOSE: To detect a bad road surely with high precision and improve the brake power on the bad road, in an antiskid braking method in which the slip rate of a wheel is calculated from the difference between a standard car body speed and the wheel speed and the hydraulic pressure supplied into the wheel cylinder of each wheel of a brake device is controlled according to the slip rate.

CONSTITUTION: In the first stage, the integration value (JD1) of the high frequency component of the accelerating speed of a car body is corrected according to the average value (FGS) of the low frequency component (75), and the slip rate is corrected according to the corrected integration value (JD2), (correction value HJDR, HJDRR), while in the second stage, the high frequency component values 71, 72, and 73 of the accelerating speed are corrected according to the accelerating speed (FGrr, FGr1) of the wheel, and the slip rate is corrected according to the high frequency component value of the corrected accelerating speed (crrection value HJDR, HJDRR).