The present invention relates to a piezoelectric resonator including: a substrate; a lower electrode (103) provided on or above the substrate; a piezoelectric member (101) provided on or above the lower electrode; an upper electrode (102) provided on or above the piezoelectric member; and a cavity (104) provided below a vibration member consisting of the lower electrode, the piezoelectric member, and the upper electrode. In the case where a resonance frequency of vibration with a thickness of the vibration member being a half of a wavelength is taken as fr1, an average of ultrasonic velocity in a material forming the cavity is taken as Vc2, and a value determined based on the resonance frequency fr1 and the average of ultrasonic velocity Vc2 is λc (=Vc2/fr1), a depth t2 of the cavity is set as shown below, (2n-1) × λc 4 - λc 8 ≦ t 2 ≦ (2n-1) × λc 4 + λc 8 , where n is an arbitrary natural number.