To calculate the speed and speed change quantity accurately and instantaneously by providing a speed-computing means to compute and estimate the speed at the time of generation of a reference signal by using stored pulse interval time.

A speed-computing means 17 computes and estimates the speed at the time of generation of a reference signal according to the pulse interval time stored in a pulse interval detecting means 13. Therefore, even when a reference signal generating means 16 operates asynchronously with a pulse generating means 11, the means 17 dose not calculate a vehicle velocity at the past timing, and it is made possible to calculate a vehicle at the time when a reference signal is generated. That is, the means 17 generates no error between the calculated vehicle velocity and actual vehicle velocity and computes the vehicle velocity accurately. In addition, a means 18 for computing speed change quantity calculates the speed change quantity on the basis of the estimated vehicle speed of the means 17, so that the vehicle speed change quantity can be also computed accurately.