To change continuously an oscillating frequency of a oscillation circuit by providing a voltage converter circuit that converts a received control voltage into a voltage whose variable range is within an unsaturation region of a transistor(TR) for control.

The voltage controlled oscillator circuit is made up of an input circuit for a control voltage given to the gate of a control P-channel TR 21 and provided with a resistor voltage divider circuit consisting of resistors 22, 23 that divide a voltage between a control voltage input terminal 24 and a fixed voltage input terminal 25 to provide the divided voltage to the gate of the control P-channel TR 21. The resistance of the resistors 22, 23 is decided properly for each TR being a component of the oscillator circuit. Then the variable range of the received control voltage is set within the unsaturation region of the TR 21. Thus, the oscillating frequency is continuously changed over the variable range of the control voltage.