PURPOSE: To omit the insertion of an attenuating device into a transmission line, to simplify the titled device and to improve its accuracy by arranging a throttle unit on the inlet of a primary radiator so that a signal is attenuated.

CONSTITUTION: A parabollic antenna 1 consists of an antenna part 11 and the primary radiator 12 and the throttle unit 13 to be optionally opened/closed is arranged on the inlet of the primary radiator 12 so as to be turned to the closing direction if an input signal level to a BS tuner 5 exceeds a prescribed value. An SHF signal (a) is received by the parabollic antenna 1 and collected to the primary radiator 12. Said collected signal is transmitted to a BS converter 4 and converted into an IF signal. The IF signal is inputted to a BS tuner 5. If the input signal level of the BS tuner 5 exceeds -28dB(mW) e.g., the SHF signal is attenuated by closing the throttle unit 13 properly to set the SHF signal to a proper signal level.