PURPOSE: To simplify the design of an amplifier circuit and the amplifier circuit itself by connecting plural differential amplifier circuits which have the same characteristics so that they have a common load, and outputting the difference signal between the sums of inputs.

CONSTITUTION: Four signals are inputted to input terminals IN11, IN12, IN21, and IN22. Then a signal -A((IN11+IN21)-(IN12+IN22)) is outputted from an output terminal OUT1 connected to the collector of the transistor(TR) Q11 of a 1st differential amplifier circuit which consists of TRs Q11 and Q12, a constant current source C1, and loads R1 and R2 and has a gain A and the collector of the TR Q21 of a 2nd differential amplifier circuit which consists of TRs Q21 and Q22, and a constant current source C2 and has no load. Further, its opposite-phase signal is outputted from an OUT 2 connected to the collectors of the TRs Q12 and Q22. Therefore, using this circuit as the initial stage of the amplifier circuit simplifies the circuit designing or the circuit itself.