An energy trap piezoelectric resonator makes use of a harmonic wave in a thickness longitudinal vibration mode and can effectively suppress a spurious fundamental wave in a thickness longitudinal vibration mode without significantly suppressing the harmonic wave that is used for the resonator. The energy trap piezoelectric resonator has a first excitation electrode disposed at an upper surface of a piezoelectric substrate polarized in a thickness direction and a second excitation electrode disposed at a lower surface, and a floating electrode disposed at at least one of the upper surface and/or the lower surface of the piezoelectric substrate so as to extend towards and away from the first excitation electrode with respect to a node of an electric potential distribution based on electric charges generated by the fundamental wave that is propagated when an energy trap vibration portion where the excitation electrodes oppose each other is excited.