PURPOSE: To make deviation of the period small sufficiently in a wide temperature range, by counting the number of pulses per a unit time fluctuated dependently upon a temperature and by setting the number of pulses adapted to the temperature to one period.

CONSTITUTION: Vibrator 1 where the peak temperature is near the normal temperature and vibrator 2 where the temperature coefficinet is larger than vibrator 1 and the peak temperature is lower than the normal temperature and the frequency at the peak temperature is high are stored in the same case 3. Gate time setting circuit 6 sends a time, when K-number output pulses of vibrator 2 can be counted, to couter 7 as a gate time and causes counter 7 to count the output of vibrator 1 to obtain value N which becomes the function of temperatures. Operator 8 obtains the oscillation frequency of vibrator 1 on a basis of an arbitrary temperature obtained from known data of vibrators 1 and 2 and holds it for a fixed time. Meanwhile, counter 10 counts successively the oscillating frequency of vibrator 1 and sends it to comparator 9 after a fixed time and causes comparator 9 to compare the oscillating frequency above with the count output of operator 8 and is rest by the coincidence output. Conseuqently, an output period which is corrected for temperature and is fixed for the time can be obtained from counter 10.