PURPOSE: To improve the reception state for a mobile body at both of a weak electric field area and a strong electric field area.

CONSTITUTION: An automatic gain control attenuation circuit 1 and a constant gain high frequency amplifier circuit 2 are provided between an antenna and a tuner section 3 and a long period initial value latch electric field strength discrimination circuit 8 controlling the automatic gain control attenuation circuit 1 is provided between them and a feedback signal from an AGC circuit 7 controls the long period initial value latch electric field strength discrimination circuit 8. When an electric field strength is weak, the attenuation in the automatic gain control attenuation circuit 1 is set to 0 to acti$ an amplifier circuit 2 at all times thereby improving the reception sensitivity. In the case of a strong electric field, since the fluctuation of the electric field strength is rapid, when the electric field strength exceeds a prescribed value, the amplifier circuit 2 is deenergized and the control of keeping the state for a prescribed period is repeated independently of the fluctuation of the electric field strength.