PURPOSE: To stabilize the temperature for a variable frequency oscillator, by securing the dependence of bias upon the temperature for a transistor which supplies the control voltage to a variable capacity diode and then cancelling the temperature characteristics of both the transistor bias and the variable capacity diode.

CONSTITUTION: The oscillating circuit 2 consists of the variable capacity diode VC, capacitor C1 and inductance L. The emitter voltage of the transistor 3 is applied to the diode VC, and the phase error voltage of the PLL loop is supplied to the base electrode of the diode VC from the input terminal 4. When the collector cut-off current ICO of the transistor 3 increases by the temperature, the emitter current IE increases to work to reduce the capacity value of the diode VC. Thus the temperature dependence is offset for a variable capacity diode that is liable to increase its capacity value by an increase of temperature.