In order to further suppress unwanted waves which may occur when the frequency (flo) of a local oscillation wave is lower than the frequency (fin) of a signal wave, the local oscillation wave is in-phase distributed between unit mixers (2a) and (2b) whereas the signal wave is opposite-phase distributed through a 180 degree distributer (4) to the unit mixers (2a) and (2b). The unit mixers (2a) and (2b) execute frequency mixing of thus distributed local oscillation wave and signal wave, and supply the result through a BRF (16a) or (16b) into a 180 degree combiner (6). The 180 degree combiner (6) effects an opposite-phase combination of outputs of the BRFs (16a) and (16b), and outputs the result. Among the unwanted waves, harmonics of the local oscillation wave are suppressed by the opposite-phase combination, the signal wave is suppressed by virtue of the BRFs (16a) and (16b), and a mixed wave of the harmonics of the local oscillation wave and harmonics of the signal wave is suppressed by the in-phase distribution of the local oscillation wave and the opposite-phase distribution of the signal wave.