On a piezoelectric board, a SAW element has first to fifth IDT electrodes and reflector electrodes with first to fourth electrode-finger narrow-pitch portions N1-N4 being formed in the respective ones of adjoining portions of the respective first to fifth IDT electrodes. An unbalanced signal terminal and balanced signal terminals are connected to the SAW element. The electrode finger pitches of the first to fourth electrode-finger narrow-pitch portions N1-N4 are formed symmetrically with respect to the third, central IDT electrode in such a manner that the electrode finger pitch of the first electrode-finger narrow-pitch portion N1 is narrower than that of the second electrode-finger narrow-pitch portion N2, while the electrode finger pitch of the fourth electrode-finger narrow-pitch portion N4 is narrower than that of the third electrode-finger narrow-pitch portion N3.