PURPOSE: To obtain stabilized temperature compensation characteristics having no linearity by converting the output from a digital analog converter to a temperature compensation digital code and correcting the nonlinearity of control voltage to frequency variation characteristics of a voltage-controlled piezoelectric oscillator by a digital analyzer circuit.

CONSTITUTION: An analog output detected by a temperature detector 1 is supplied by the analog digital (A/D) converter 2 and converted into the digital code, which is supplied to a memory circuit 3. The digital linearizer circuit 5 corrects the nonlinearity of control voltage to frequency variation characteristics of the voltage-controlled piezoelectric oscillator 6. The memory 8 is stored previously with data for correcting the nonlinearity of control voltage to frequency variation characteristics of the voltage-controlled piezoelectric oscillator 6. The digital code in the memory circuit 8 is supplied to a converter 9 to obtain a nonlinearity corrected analog signal. The output signal of the circuit 5 is supplied to the voltage-controlled piezoelectric oscillator 6 to correct frequency temperature compensation and control voltage to frequency variation characteristics digitally.