To provide an AGC circuit capable of enlarging the change quantity of a gain in respect to the variable quantity of an AGC voltage by preventing a source potential from being lowered even when the drain current of a dual gate type field effect transistor(FET) provided in the AGC circuit is changed.

A circuit part 3 for bias is connected to a source terminal S of an FET Q1. Between the source terminal S and a ground terminal, the serial circuit of resistors R4 and R5 is connected, the node of the resistors R4 and R5 is connected to the base of a transistor Q2, the emitter of the transistor Q2 is grounded and the collector is connected through a resistor R6 to a power source VDD. Besides, the power source VDD is successively connected through the collector and emitter of a transistor Q3 to the source terminal S and the collector and base of the transistor Q3 are respectively connected to both the terminals of the resistor R6.