To reduce the noise of a high frequency component by providing the hysteresis characteristic with respect to a received electric field level to a control circuit receiving the received electric field level and controlling an electronic attenuator.

A detection demodulation circuit 3 detects an electric field level to discriminate whether or not the electric field level is higher than a prescribed level such as 40dB(μV), and to discriminate whether or not the electric field level is lower than a prescribed level such as 30dB(μV) when the electric field level is lower than the 40dB(μV). When whether or not the electric field level is lower than the 30dB(μV), a control circuit 7 provides the output of an H level to a base of a transistor (TR) 11 thereby decreasing a treble control voltage. When the electric field level is more than the 30dB(μV) and less than the 40dB(μV), the hysteresis characteristic is provided to the control circuit 7 to keep the existing operation so long as the electric field strength is fluctuated between the range above. When the treble control voltage applied to an electronic attenuator 4 is increased, the boost level of a high boost circuit 4b in the inside of an IC is increased and when the applied voltage is decreased, the boost level is decreased.