PURPOSE: To eliminate disadvantage due to static electricity and to suppress the fluctuation of a bias voltage of an input section of a converter by providing a filter circuit comprising an inductive element and a capacitive element between a plane antenna and an amplifier circuit.

CONSTITUTION: The filter circuit F consists of the inductive element L11 connecting a transmission line 13 and ground and the capacitive element C11 connected between the inductive element L11 and a post-stage of a connecting point of the transmission line 13 and provided between the plane antenna 11 and a low noise amplifier circuit 15. Since the inductive element L11 grounds the plane antenna 11 and ground in terms of DC, a low frequency noise such as static electricity or lightning surge invaded from the plane antenna is escaped to ground. A reception signal from the antenna 11 has a high frequency, then the signal is not led to ground through the inductive element L11 but sent to the converter 12. Moreover, the capacitive element C11 cuts off the plane antenna 11 and the low noise amplifier circuit 15 in terms of DC, then the fluctuation of the bias voltage is suppressed.