PURPOSE: To perform the high-speed changeover of a frequency at all using temperatures by changing the offset voltage of a control voltage applied to a voltage controlled oscillator corresponding to an ambient temperature in a temperature variable offset type amplifier circuit.

CONSTITUTION: When the fluctuation of the temperature is generated at the time of the same control voltage by the temperature characteristics of the voltage controlled oscillator 1, the fluctuation of an output frequency is generated. Then, in the temperature variable offset type amplifier circuit 8, input from an offsetting circuit 7 worked so as to cancel frequency fluctuation for temperature fluctuation from initial setting by an element (thermister, for instance) for which the fluctuation of characteristics is generated corresponding to the temperature present in the input part of the output of the offsetting circuit 7 is inputted to an amplifier part, amplified and added with the output of a phase detector 5 and the control voltage corresponding to the temperature fluctuation is outputted. Then, by the control voltage outputted from the temperature variable offset type amplifier circuit 8, the voltage controlled oscillator 1 is set at the output frequency for which the temperature characteristics are corrected, that is a desired frequency, when a loop at the time of frequency changeover is open.