PURPOSE: To simplify a constitution and to freely execute the individual adjustment of respective coefficients by impressing the output of a proportionate amplifier to one edge of a variable capacity diode and impressing the output of an integration circuit to other edge of a variable capacity diode.

CONSTITUTION: The title circuit is equipped with a voltage controlled oscillator(VCO) 8 to control an oscillation frequency by the voltage impressed to a variable capacity diode(VCD) 7. In such a constitution, the phase of an oscillation output OUT of the VCO 8 and an external input signal Si is compared with a phase comparator 2, the output is proportionately amplified by a proportionate amplifier 3 and impressed through a resistor 9 to one edge of the VCD 7. The output of the phase comparator 2 is also inputted and integrated to an integration circuit 4, impressed through a resistor 10 to other edge of the VCD 7 and thus, the transmission phase of the VCO 8 is synchronized to the phase of the external input signal Si. Consequently, by respective outputs of the proportionate amplifier 3 and the integration circuit 4, the inter-terminal voltage of the VCD 7 is directly specified, an adding circuit 5 is made unnecessary and the individual adjustment of respective coefficients can be freely executed by resistors 9 and 10.