PURPOSE: To enable the temperature compensation of an oscillator over a wide range, by changing the gain of a DC amplifier through the operation of a temperature switch, in accordance with the temperature detected by a temperature sensor.

CONSTITUTION: The gain of an amplifier 3 is changed by controlling the feedback amount of a feedback circuit consisting of temperature switches TS1, TS2 and resistors R1∼R5 by an output of a temperature sensor 2. The temperature switches TS1, TS2 consist of e.g. a temperature rapid change element, and they are at short- circuit or low resistance state at a low temperature, but at open or high resistance when temperature reaches T1°C and T2°C(T1<T2) respectively. Thus, the resistance of the feedback circuit of the amplifier 3 is the lowest at ≤T1°C, the highest at ≥T2°C, and intermediate at T1∼T2°C. Further, the change in a bias voltage VB being the output of the amplifier 3 is gentle at ≤T1°C, steep at ≥T2°C, and intermediate at T1∼T2°C. Thus, the oscillating frequency of a voltage controlled oscillator 1, e.g. can be kept constant over a wide temperature range.