PURPOSE: To attain high stabilization by inputting two control signals to a voltage controlled oscillator, applying a high temperature compensation voltage on one of them, and decreasing the quantization error of an application temperature compensation voltage on the other side.

CONSTITUTION: The output of a temperature detector 1 is supplied to an analog/ digital converter 2 and an analog circuit network 6. Quantization is performed by supplying the large change of temperatures T1-T2 to the analog circuit network 6, and supplying only the change of curvature from which the large change is subtracted to the analog-digital converter 2. Therefore, the error width of the quantization error can be reduced by decreasing the amplitude of voltage change to be quantized, and characteristic with low ripple can be obtained in frequency characteristic.