A circuit module includes a duplexer mounted on a module board and a cover layer is stacked on an insulating layer that is disposed on one principal surface of a device board so as to enclose a predetermined area thereof. A transmission filter device and a reception filter device that have different transmission bands are provided on the one principal surface of the device board in the predetermined area thereof within the space enclosed by the insulating layer between the device board and the cover layer. Accordingly, the duplexer does not include a package board as in the existing technique, and in turn a circuit module including the duplexer mounted on the module board is significantly reduced in height and in size.