a strip piezoelectric ceramic substrate having first and second principal surfaces facing each other, having a longitudinal direction and a width direction vertical to the longitudinal direction, and polarized in the longitudinal direction;

a first excitation electrode extending in the width direction of the piezoelectric ceramic substrate at a substantial longitudinal center part of the first principal surface of the piezoelectric ceramic substrate; and

a second excitation electrode overlapping the first excitation electrode through the piezoelectric ceramic substrate at the substantial center part of the piezoelectric ceramic substrate of the second principal surface of the piezoelectric ceramic substrate,

wherein portions of the first and second excitation electrodes overlap in the longitudinal direction define an excitation region excited in response to application of an alternating electric field and portions of the first and second excitation electrodes not overlapping define a non-excitation regions,

wherein the non-excitation regions neighboring the excitation region have (a) the same polarization axis direction as the excitation region and a polarization degree whose absolute value is smaller than an absolute value of a polarization degree of at least one of the excitation region and unpolarized regions, (b) a Young's modulus smaller than that of the excitation region, or both (a) or (b),

whereby an energy-trapping piezoelectric vibration portion utilizing a third harmonic overtone of a thickness shear mode is formed.