the branch circuit and the transmitting side lc parallel resonant type filter which eliminates necessities of the corresponding matching circuits for performing matching adjustment therefore the duplexer is further miniaturized in addition wiring loss can be each improved between the branch circuit and the receiving side lc parallel resonant type filter between the receiving side lc parallel resonant type filter and the surface acoustic wave filter and between the branch circuit and the transmitting side lc parallel resonant type filter accordingly the overall loss of the duplexer is greatly minimized furthermore the connection of each of the branch circuit the receiving side lc parallel resonant type filter the surface acoustic wave filter and the transmitting side lc parallel resonant type filter can be provided in the multi layer substrate therefore furthermore miniaturization of the duplexer is achieved as in the duplexer in fig6 when the branch circuit is constructed using the balun element both of the third terminal connected to the transmission circuit observed from the second terminal connected to the reception circuit and the second terminal observed from the third terminal are open in terms of a high frequency therefore since complete isolation can be obtained between the second terminal and the third terminal the reception signal is prevented from interfering with the transmission signal side and vice versa consequently the reliability of the duplexer is greatly.