A duplexer includes a transmit filter connected between a common terminal and a transmission terminal, a receive filter connected between the common terminal and a reception terminal, a capacitor connected in parallel with one of the transmit filter and the receive filter and provided between two terminals of the common terminal, the transmission terminal, and the reception terminal, and a package. The package includes an insulating layer, foot pads that include the common terminal, the transmission terminal and the reception terminal and are formed on one surface of the insulating layer, and interconnections formed on another surface opposite to the one surface of the insulating layer. The capacitor is composed of two capacitor forming units that are connected in parallel with each other and are formed with at least one foot pad of the foot pads and two of the interconnections that overlap with two opposing sides of the at least one food pad respectively.