The present invention provides a duplexer using a ladder-type filter, which has a small size and is superior in isolation characteristic, and a communication apparatus using such a duplexer. A series resonator (R1) contained in a first filter element (F1) and a parallel resonator (R4) contained in a second filter element (F2) are disposed so as not to allow the elastic wave propagating paths to be overlapped with each other. By disposing them in this manner, it is possible to prevent an elastic wave, leaked from the series resonator (R1) and most influential to the isolation characteristic, from being received by the parallel resonator (R4). Consequently, it is possible to achieve a small-size duplexer that is superior in isolation characteristic.