PURPOSE: To obtain high frequency stability over a wide temperature range by devising the oscillator such that a temperature compensation element section makes analog temperature compensation and a variable capacitive element section whose capacitance is varied with a control voltage added to the temperature compensation element section makes digital temperature compensation in addition.

CONSTITUTION: When temperature around a crystal vibrator 33 changes, a temperature sensor detects the change and a temperature compensation element section 32 also detects it. The temperature compensation element section 32 makes analog temperature compensation so that a frequency fluctuation of the crystal vibrator 33 is set within a range from ±2ppm to ±3ppm (at -30°C to +80°C). Then a control voltage is applied to a variable capacitive element section 31 via a digital circuit network according to the temperature information detected by the temperature sensor. Since the variable capacitance element section 31 is controlled by the control voltage, the frequency fluctuation of the crystal vibrator 33 is set within a range of ±0.15ppm (at -30°C to +80°C).