PURPOSE: To dispense with exchange of a sensor rotor or a controller even at changing a wheel diameter and the like by providing a correcting signal output means capable of selectively changing over corresponding to at least either a wheel diameter or the speed change ratio of a transmission, and computing an appropriate wheel speed.

CONSTITUTION: Wheel speed sensors 9 to detect teeth train forms on the circumference of rotors rotating together with rotor shafts with opposed pick up sensors and output pulse signals are respectively provided on the rotor shafts connected to respective wheels of a vehicle. Wheel speeds are computed with a controller 8 based on these pulse signals. When a wheel diameter or the speed change ratio of a transmission is changed, a correcting signal is output with a frequency exchange circuit 8d capable of selectively changing over with a changeover switch 8b. Hereby, the wheel speed fitting in the wheel diameter or the speed change rario is always correctly computed and output to a ABS control circuit 8e, and hereat the slip quantities of respective wheels are obtained from wheel acceleration of respective wheels and a reference vehicle body speed, so as to regulate the brake pressure.