To improve the suppression degree of the AM demodulation output level due to interference signals to prevent the deterioration of the sensitivity.

When an RF amplifier 2 amplifies inputted interference signals to output signals, the interference signal output level of an RF level detector 3 rises to exceed a set value of the amplifier 2 to result in the reduction of the amplification degree of the amplifier 2. This lowers the output level of desired signals from the amplifier 2 and also the desired signal output level of an intermediate frequency filter 6. This filter 6 cuts off the interference signals and hence the output level of an IF level detector 6 lowers according to the desired signal output level of the filter 6. The amplification degree of an AF amplifier 9 increases when the output of the RF level detector 3 is higher than the voltage value of a comparison voltage source of the AF amplifier 9 and the output of the IF level detector 10 is lower than the voltage value of the comparison voltage source of the AF amplifier 9.