PURPOSE: To calculate a wheel speed almost instantaneously by a simple circuit by using two dividers, two counters, and an operating device in combination.

CONSTITUTION: An operating device 4 is provided which outputs the digital value of a wheel speed on the basis of a wheel speed signal R generated by the signal of a wheel speed sensor 8. A divider 1 counts a high frequency f0 and, every time its count value reaches a certain value, generates one pulse. The pulse is counted by a counter 1 in a period relating to the period of the signal R. On receiving the count value through the operating device 4, a divider 5 counts the high frequency f0 and, every time its count value becomes equal to the output of the counter 1, generates one pulse. This pulse is counted by a counter 6 in the period of the signal R and the resulting count value is supplied to the operating device 4. When the count value of the counter 6 is not equal to a constant digital value, the output of the operating device 4 is corrected by its differnce. Thus, the simple circuit calculates the wheel speed almost instantaneously.