To avoid defects due to the oscillation defect or stop of a tuning fork crystal vibrator by means of a laser irradiation by providing a part where the mass is not removed between the mass removing part of a frequency adjusting pattern and a side surface electrode just near it.

PEQ is a tuning fork crystal vibrating piece and an outer shape and an electrode are formed on a crystal wafer by etching by a photo lithography. The spot of a YAG laser is controlled to a 60 μm diameter and trimming is executed by the laser irradiating part 9 of a coarse adjusting part 4 which is formed in the tip of a vibrating part where a mass reducing effect in frequency adjustment is large. After coarse adjustment, the spot of the laser is converged to a 20 μm diameter and adjusted to a target Margins 6 as against the side surface electrode are provided in the width direction of the vibrating part 2 so as to irradiate the laser. A laser working width is set at the inner side of the width direction of the vibrating part 2 from the both end parts of the vibrating part 2 in PEQ with the respective margins being 60 μm in width.