PURPOSE: To make it possible to supply the best gate bias to an apparatus with a high-frequency circuit by reversely biasing between the gate and source of FET on the basis of the output of a rectifying method of rectifying the output of a sine wave generating method.

CONSTITUTION: High frequency (RF) input (f0) is applied to mixing method 1 through input capacitor C0. Local oscillating stage 2 consists of transistor Q0, etc., applied with the output of tank circuit 3, and the emitter output of transistor Q0 is positively fed back by way of a electrostatic capacity divider circuit composed of capacitors C5 and C6 so as to extract sine-wave output (fosc). Further, rectifier circuit 4 consists of capacitor C10 holding the peak value of diode D0. Mixing stage 1 consists of a tuning circuit composed of common-source N-channel depletion MOSFETM0, capacitor C8 and coil L0. To gate G of FETM0, output-V of rectifier circuit 4 is applied by way of resistance R7.