PURPOSE: To suppress generation of distortion and also to prevent deterioration of an S/N ratio, by controlling the gain at the first stage in case when an input level is high, and controlling the gain between stages in case when the input level is low.

CONSTITUTION: In case input voltage to a terminal is low, output voltage of a detector 20 is low, too. Therefore, voltage applied to a Zener diode 40 becomes Zener voltage or below. This voltage is applied to variable attenuators 10∼12 provided between stages of an amplifier and attenuates an input signal. In this case, the potential across a Zener diode 41 is kept constant by Zener voltage, therefore, a diode 13 conducts, and attenuation at the first stage is eliminated. When the input voltage is high, the potential across the Zener diode 40 becomes Zener voltage, the attenuation quantity of the attenuators 10∼12 is made constant, also the potential across the Zener diode 41 becomes Zener voltage or below, and in accordance with the input voltage, the attenuation quantity of the attenuator 13 of the first stage is controlled.