Disclosed is an energy-trapping-by-frequency-lowering-type piezoelectric-resonance device utilizing a higher harmonic in the mode of thickness-extensional vibration, in which at least three electrodes for energy trapping are arranged so as to be overlapped with each other in the direction of thickness of layers of piezoelectric material forming a plate-shaped body. The three electrodes comprise a pair of outermost electrodes and at least one inner electrode. The diameter of one polygonal side of at least one outermost electrode is made larger than the diameter of one polygonal side of an inner electrode.
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