A duplexer having a filter and an isolation part which are integrally formed including a substrate, a transmitter filter integrated on the substrate to pass signals only in a frequency band for transmission, a receiver filter integrated on the substrate to pass signals only in a frequency band for reception, and an isolation part integrally formed with either one of the transmitter filter and the receiver filter to isolate the signals passed through the transmitter filter and the receiver filter from each other. Since the isolation part is integrally formed with either one of the transmitter filter and the receiver filter, the duplexer can be manufactured in a small size by simplified processes.