PURPOSE: To suppress the gain change in the AC component against the fluctuation of the DC component by inserting a current mirror circuit to each emitter of transistors (TR) of a differential pair circuit whose gain is controlled by a control voltage fed to the base.

CONSTITUTION: Current mirror circuits comprising respectively a diode Q3 and a TR Q4 and a diode Q5 and a TR Q6 are connected in parallel with Ont. TRS Q1,Q2 being the differential pair being subjected to gain control respectively. In selecting the emitter area ratio of the TRS Q1∼Q4 as Q3:Q4=Q5:Q6=1:n, the current mirror ratio is (n), output currents Iout1, lout2 of the amplifier circuits are branched as 1:n by the current mirror circuits, and the collector current of the TRs Q1,2 is l/(1+n) of the output currents Iout1,Iout2. Thus, the error by the collector current difference is decreased to l/(l+n) and the fluctuation of the AC component is decreased against the fluctuation of the DC component.