PURPOSE: To obtain a tuning voltage of high accuracy, by providing a phase shifter in which a frequency versus phase shift characteristics is freely changeable and generating the tuning voltage in response to a DC component level of a mixed output between a phase shifter output and a specified signal.

CONSTITUTION: A phase shift output from a phase shifter 1 taking a rectangular wave train of 50% duty as an input is converted into a rectangular waveform of 50% duty having a prescribed repetitive frequency f0 again at a waveform shaping circuit 2 and becomes one input of an OR circuit 3. A circuit input signal IN is applied to another input to the OR circuit 3 and a mixed signal of both input signals is obtained from the output of the OR circuit 3. This mixed signal is inputted to an integrator 4 to obtain the DC component, which is applied to an operational amplifier OP. The component, after being inputted to the operational amplifier OP, is compared at a prescribed reference voltage E0, and an amplified output in response to the difference voltage is obtained. This amplified output becomes a control voltage (turning voltage) of an electronic tuning circuit consisting of a varactor D0 and a coil L0 via a resistor R1.