PURPOSE: To provide a piezoelectric resonator applied to a desired harmonic region by suppressing the excitation of a fundamental wave without giving effect on the stimulation of a ternary harmonic wave.

CONSTITUTION: In the energy confinement type piezoelectric resonator 1 utilizing harmonic vibration being a thickness longitudinal vibration of a stimulated part formed to a piezoelectric substrate 2 having a short side and a long side, the size of the short side of the piezoelectric substrate 2 is set between the stimulation region of the fundamental wave and the stimulation region of the ternary harmonic wave and a region linked to both the front and rear sides at the outside of the short side of the piezoelectric substrate 2 and both the front and rear sides of the stimulated part is formed to be a cavity 6. Thus, the stimulation of the fundamental wave is suppressed without giving effect on the stimulation of the ternary harmonic wave and the suppression of the stimulation of the ternary harmonic wave due to the provision of the cavity as above is avoided.