PURPOSE: To execute accurate correction by providing first to third operating means even when a wheel speed pulse inputted from a sensor is missing for some reason.

CONSTITUTION: In the first operating means (d), allowable cyclic fluctuating amplitude is set from a wheel speed pulse with the precedent wheel speed pulse cycle stored in a storing means (c) as a core. In the second operating means (e), from the upper limit value of the allowable cyclic fluctuating amplitude of the wheel speed pulse cycle set in the first operating means (d), a missing pulse number considered to be a true pulse number involved in the one cycle of the wheel speed pulse cycle measured this time is introduced. In the third operating means (f), from the lower limit value of the allowable cyclic fluctuating amplitude of the wheel speed pulse cycle set in the means (d), the missing pulse number is found and is compared with the lacking pulse number introduced by the means (e) and when the missing pulse number more approximate to the true pulse number is lower than the lower limit value of the allowable cyclic fluctuating amplitude, the allowable cyclic fluctuating amplitude is reset again. Thus, the correction of the missing pulse is executed.