PURPOSE: To attain the precise machining of the tuning fork part of a piezoelectric vibrator by masking the tip part of a tuning fork excluding a slit, applying the accelerated particles to the deepest part, and shaving off the deepest part or the tip part of the tuning fork.

CONSTITUTION: A slit 4 is masked by a mask member 8 end the accelerated particles of the silicone sand or an abrasive material, etc., are applied to a tip part 3a of an end part 3 of a piezoelectric substrate 2 excluding the slit 4 as shown by an arrow X. Thus the part 3a is shaved off by the particles and therefore the cut depth l of the slit 4 is gradually reduced. Then the part 3a of the substrate 2 excluding the slit 4 is masked by the mask members 10 and 11, and the accelerated particles are applied to the deepest part 4a of the slit 4 as shown by an arrow Y. Thus a tuning fork part is machined with high precision and the piezoelectric vibration frequency is set with high accuracy.