A diplexer includes a first filter circuit including a first loop inductor defining a first loop plane and a second loop inductor defining a second loop plane, a second filter circuit adjacent to the first filter circuit, and a first via hole conductor that electrically connects an input/output terminal, the first filter circuit and the second filter circuit to each other. The first loop plane faces the second loop plane while protruding beyond the second loop plane in a first direction. The first via hole conductor is provided relative to the first loop inductor in a second direction from the first loop plane toward the second loop plane, and is superposed with a portion of the first loop plane that protrudes beyond the second loop plane when viewed in the second direction.