A mixer for tuning to an intermediate frequency signal, an intermediate frequency amplifier provided at a rear stage of the mixer, an intermediate frequency tuning circuit interposed between the mixer and the intermediate frequency amplifier for tuning to the intermediate frequency signal, and a trap circuit interposed between the mixer and the intermediate frequency amplifier for attenuating the signal of an adjacent channel are comprised. By connecting a first switch means to the trap circuit in parallel to turn on the first switch means, the RF characteristic at an input port of the intermediate frequency amplifier or an output port of the mixer can be observed, without being influenced by the trap circuit.