PURPOSE: To achieve a higher accuracy with a higher noise compression effect, by arithmetically averaging the number of pulses and a section time separately to determine a speed or an acceleration of a vehicle rotating section from an average number of pulses and an average section time.

CONSTITUTION: An antiskid brake system is made up of an object 10 desired to detect rotation provided on a wheel, a magnetic sensor 12 as opposed to the object 10, a speed/acceleration detector 14 for detecting a speed and acceleration of the wheel from an output of the sensor 12 and a brake controller 18 for controlling a brake oil pressure to a brake cylinder 16 from the speed and acceleration thus detected. The speed/acceleration detector 14 has a speed pulse generation circuit 20, a measuring circuit 22 for the number of speed pulses and a section time and a speed/acceleration computing circuit 24. Then, the number of speed pulses and the section time are arithmetically averaged separately to determine the speed and acceleration from the average number of pulses and the average section time.