To facilitate circuit integration by adding a temperature detection value and an approximated ternary curve output value so as to generate a control signal of a voltage controlled crystal oscillator thereby smoothly changing an input voltage to the oscillation circuit with respect to the temperature change continuously.

An approximate ternary curve generating circuit 2, a temperature detection circuit 1, a constant voltage generating circuit 3 generate each prescribed voltage respectively and dispersion among the individual voltages in a ternary coefficient α, a gradation β in the temperature characteristic and a frequency offset γ is fine-adjusted by changing gains of programmable gain amplifiers 4, 5, 6. Each voltage after the fine-adjustment is added by an adder circuit 7 to obtain a control voltage of a voltage controlled crystal oscillator circuit 8 corresponding to the frequency characteristics with respect to the temperature of the crystal vibrator and the control voltage is fed to the oscillation circuit 8. Thus, the temperature characteristics of the crystal vibrator is accurately compensated.