PURPOSE: To obtain measurement precision within a constant range at any time regardless of a vehicle speed by setting a pulse period corresponding to a specific vehicle speed previously, and measuring the period of frequency- divided pulses by a counter and measuring the vehicle speed.

CONSTITUTION: A frequency dividing means 4 consists of the counter 7 which counts pulses from a vehicle speed sensor 2, a data register 8 for comparison in which a frequency division value supplied from a CPU5 is stored, and a comparator 9 which compares the value of the data register 8 with the value of the counter 7 and interrupts a CPU5 when the value of the counter 7 becomes equal to the frequency division value to start the calculation of the vehicle speed. The frequency division value set in the data register 8 for comparison is a frequency division value for frequency division of pulses from a vehicle speed sensor 2 and the CPU5 calculates the period of the frequency-divided pulses from the value of a timer counter 3 and find the period of pulses from the vehicle speed sensor 2 on the basis of this calculated value and frequency division value to calculate the vehicle speed.