PURPOSE: To remove the waveform distortion due to an in-phase signal by using a differential amplifying circuit.

CONSTITUTION: A constant voltage is impressed to the base of a Tr Q5 by a transistor Tr Q6, the voltage and a voltage VG of a gain control terminal 5, which is the base of a Tr Q7 to constitute the Tr Q5 and a differential amplifier are differentially amplified and the current flows at the collector of the Tr Q5. When input terminals 1 and 2 and signals VIN 1 and VIN 2 are inputted, they are differentially amplified by Tr Q1 and TR Q2 to constitute the differential amplifying circuit and an output VOUT 1 of a positive phase and an output VOUT 2 of a negative phase are respectively outputted 3 and 4. An AGC circuit gain at such a time is determined by a collector current to flow at the Tr Q1 and Q2, and the collector current to flow at the Tr Q1 and Q2 is determined by the collector current of the Tr Q5. Since the collector current is changed in accordance with a voltage VG, the gain of the AGC circuit is changed in accordance with the voltage VG.