A multiplexer includes filters on one principal surface of a mounting substrate and having mutually different frequency bands, and an inductance element which is incorporated in the mounting substrate and one end of which is connected to one end of the filter. The other end of the inductance element and one end of each of the filters, are connected to each other at a common connection point. The inductance element is defined by spiral wiring conductors disposed in first and second wiring layers provided in an inner layer of the mounting substrate. The mounting substrate includes third and fourth wiring layers which are adjacent to the first and second wiring layers, and in which no ground pattern is provided in a portion corresponding to a formation region of the inductance element.