PURPOSE: To make it easy to generate bulk waves in the direction vertical to the surface and improve independence of each pair of cross finger electrodes by forming a notched groove between cross finger electrodes.

CONSTITUTION: Notched grooves 4 are provided between cross finger electrodes 2 and 3 from the surface of a piezoelectric material plate 1. When the piezoelectric material plate 1 is polarized in both sides of these notched grooves 4, distribution of polarization is across these notched grooves 4. Distribution of polarization has a sharp angle to the surface of the piezoelectric material plate 1. Thus, it is difficult to generate surface waves, and surface waves are prevented from being propagated on the surface of the piezoelectric material plate 1 by these notched grooves 4, and required bulk waves are generated efficiently in the direction of an arrow.