PURPOSE: To enable temperature compensation of wide variety with one oscillator, by selecting the effective electrode of piezoelectric oscillator according to temperature for temperature compensation.

CONSTITUTION: An electrode d1 is formed at the center of one plane of a crystal oscillator D, and the electrode d2 at the center and the electrode d3 at the circumference are formed on another plane. Further, the thermister Th, resistor R2 and the voltage of the power supply E set to the output of a comparator CM, for example, 1 at ≤20°C and 0 at ≥20°C. Thus, the switching circuit S1 is on at ≤20°C and the electrode d2 is operated as the effective electrode, and the switching circuit S2 is on at ≥20°C and the electrode d3 is operated as the effective electrode. Thus, very stable oscillation can be held.