To adjust the resonance frequency of a piezo-resonator to an object frequency while suppressing production of an in-band ripple.

The frequency adjustment method for the piezoelectric resonator 1 comprises a process for preparing the resonator 1 where first and second vibration electrode 3, 4 are formed on both major sides of a piezoelectric substrate 2 and the thickness of the 1st vibration electrode 3 is formed thicker than the thickness of the 2nd vibration electrode 4 and a process for processing the 1st or 2nd vibration electrode to have a desired frequency in a direction that both thicknesses of the first and second vibration electrodes 3, 4 are equal to each other.