To obtain a high-precision and high-reliability tuning-fork type crystal vibrator, which is greatly reduced in manufacture cost and has superior aging characteristics.

A crystal element piece 2 in a tuning-fork shape having two arm parts is prepared and electrodes 5a to 7a and 5b to 7b are filmed on the top surface of the crystal element piece to provide overlapped parts 9a and 9b, where the crystal surface is exposed at the tips of both the arm parts. The overlapped part surfaces are partially removed to have their frequency adjusted, by having the overlapped parts with reactive ionized particles irradiated by a reactive ion etching device which uses chlorofluorocarbon Freon gas as the ion source. Consequently, the frequencies are adjusted, by reducing the mass of the material itself of the crystal vibrating piece, thus, the overlapped parts need not be provided with electrode films, the production efficiency is improved by a great decrease in man-hours, and the manufacture cost is greatly reduced by a great decrease in the amount of an electrode material in use. Furthermore, a high-precision and high-reliability tuning-fork type crystal vibrator with superior aging characteristics is obtained.