Abstract: An automatic gain control circuit of an amplifier 1 having a gain control function is provided with a signal-to-noise detection circuit 2 which detects a signal-to-noise ratio of an output signal and an AGC setting circuit 3 which sets the gain of the amplifier 1. The AGC setting circuit 3 determines the AGC gain according to the level of an input signal and the signal-to-noise ratio detected by the signal-to-noise ratio detection circuit 2. In a region where there is a large AGC gain and where the signal-to-noise ratio is reduced by the AGC circuit, the level of an output signal is increased so as to render the signal-to-noise ratio of the output signal constant. Even if an input electric field is reduced by a fading phenomenon and if there is an increase in the AGC gain, there is prevented a decrease in the signal-to-noise ratio due to an increase in the noise floor stemming from the AGC circuit itself, thereby preventing deterioration of the receiving sensitivity of the automatic gain control circuit.