Patent ID: 8368486

Claim:
A duplexer comprising: an acoustic wave element having an antenna terminal and two balanced output reception terminals, and a transmission terminal; a substrate mounting the acoustic wave element on the surface; a first columnar conductor electrically connected to the antenna terminal and drawn to a back surface of the substrate; a second columnar conductor electrically connected to one of the reception terminals, and drawn to the back surface of the substrate, while being buried partially in the substrate; a fourth columnar conductor electrically connected to the other of the reception terminals, and drawn to the back surface of the substrate, while being buried partially in the substrate; a first ground pattern region arranged between the first columnar conductor drawn part and the second columnar conductor drawn part, on the back surface of the substrate; and a second ground pattern region electrically connected to the first ground pattern region and arranged in the part not including the part between the first columnar conductor drawn part and the second columnar conductor drawn part, on the back surface of the substrate, wherein if the second columnar conductor drawn part and the fourth columnar conductor drawn part are different in distance to the first columnar conductor drawn part, a density of a columnar conductor electrically connected to the first ground pattern region is set higher than a density of a columnar conductor electrically connected to the second ground pattern region.