In an automatic gain control circuit, a peak detection circuit detects and outputs the peak voltage of an output signal from a variable gain circuit. An average value detection/output amplitude setting circuit detects the average value voltage of an output signal from the variable gain circuit, and outputs a voltage obtained by adding a voltage with an amplitude 1/2 a desired output amplitude of the variable gain circuit to the average value voltage. An amplification circuit controls the gain of the variable gain circuit by amplifying the difference between the output voltages of the peak detection circuit and average value detection/output amplitude setting circuit and outputting a gain control signal to the variable gain circuit. The number of base-emitter junctions of transistors on a path in the peak detection circuit from input ports which receive output signals from the variable gain circuit to an output port which outputs a voltage to the amplification circuit is equal to the number of base-emitter junctions of transistors on a path in the average value detection/output amplitude setting circuit from input ports which receive output signals from the variable gain circuit to an output port which outputs a voltage to the amplification circuit.