A diplexer contains a common terminal connected to an antenna, a first input/output terminal for inputting/outputting signals of a plurality of high frequency bands higher than a predetermined frequency, and a second input/output terminal for inputting/outputting signals of low frequency bands lower than the predetermined frequency. Between the common terminal and the first input/output terminal, a high pass filter and low trap circuits for attenuating the low frequency bands respectively are interposed in series, and, between the common terminal and the second input/output terminal, a low pass filter and high trap circuits for attenuating the high frequency bands respectively are interposed in series.
