PURPOSE: To expand the variable range of an oscillating frequency by oscillating a frequency in response to a difference between phase angles of a resultant vector and the 1st voltage vector with the resultant vector supplied to a tank circuit after the band limit is processed to the resultant vector formed in the ratio in response to a control signal.

CONSTITUTION: Differential amplifiers 12, 13 constitute a circuit composing two vectors (e1-e2) and -e1 and a resultant vector e4 composed in the ratio of the control voltages at terminals 3, 4 is extracted from an emitter of a transistor (TR) Q9. The resultant vector e4 is expressed in equation. The resultant vector e4 is fed to a low-pass filter 5 comprising a resistor R3 and a capacitor C3 from the emitter of the TRQ9, an unnecessary harmonic is eliminated at the filter 5 and also the signal is fed to the tank circuit 1 while being phase-shifted. The tank circuit 1 is oscillated in a frequency in response to the phase difference between the resultant vector supplied from the low-pass filter 5 and the voltage vector e1.