PURPOSE: To obtain a large IF signal and to eliminate the need for an independent trap circuit, by coupling a buffer amplifier having a choke load and a mixing amplifier with a capacitor, and selecting an inductance of the choke load and a capacitance of a coupling capacitor to a value capable of resonance with an intermediate frequency.

CONSTITUTION: An amplifier 3 which buffers and amplifies a local oscillating signal has a choke load 18, and is coupled to the 2nd gate of a dual gate MOSFET10 via the coupling capacitor 19. An RF signal is applied to the 1st input of an FET10 via a terminal 15. The inductance of the choke 18 and the capacitance of the capacitor 19 are selected to a value capable of resonance with the intermediate frequency.