To provide a frequency adjustment method for a piezoelectric wafer composed of plural piezoelectric vibration pieces of tuning-fork type with a pair of vibration arms extending from a base section which are coupled into an integral body, to adjust the frequency of the piezoelectric vibration pieces of tuning-fork type therein to a target frequency.

The frequency adjustment method comprises a step (S11) of forming a first metal (24) in at least part of a frequency adjustment section formed at the tip of vibration arms, a step (S12) of measuring the frequency of piezoelectric vibration pieces of tuning-fork type attached to a piezoelectric wafer (200), and steps (S13-S15) which, when the measured frequency of the piezoelectric vibration pieces of tuning-fork type is lower than a target frequency, shave off the first metal (24) formed in the frequency adjustment section and, when the measured frequency of the piezoelectric vibration pieces of tuning-fork type is higher than a target frequency, sublime a second metal (302) disposed apart from the piezoelectric vibration pieces of tuning-fork type to deposit a sublimate on the frequency adjustment section.