PURPOSE: To stabilize the operation of a voltage controlled oscillator and to prevent step out from being generated by providing an ambient temperature detecting means at a phased locked loop oscillation circuit provided with the voltage controlled oscillator, and impressing a voltage corresponding to a detected temperature on the voltage controlled oscillator as a control voltage.

CONSTITUTION: When an ambient temperature is raised, an analog signal is generated in an ambient temperature detector 7, and it is converted to a digital signal by an A/D converter 8, and is inputted to a memory circuit 9. The digital signal corresponding to the one is outputted from the circuit 9, and it is recovered to the analog signal by a D/A converter 10, and is inputted to the voltage controlled oscillator 4, and a variable capacitance device 5 is controlled by the output of the oscillator, then, oscillation output not being affected by the change of the ambient temperature can be obtained. Also, when the ambient temperature drops, a reverse voltage is impressed on the device 5, and the oscillation output not being affected by the ambient temperature can be obtained similarly. Therefore, no change is generated in a frequency and the step-out can be prevented from occurring.