PURPOSE: To provide a frequency control method of an AT vibrator which can improve the reliability and the productivity of the AT vibrator.

CONSTITUTION: The energy of the ultraviolet light emitted from an excimer laser device 1 is controlled and an electrode film 6 formed on the main surface of an AT vibrator 5 is irradiated by the ultraviolet light. Thus the film 6 is dissociated by a necessary extent so that the oscillation frequency of the vibrator 5 is controlled. In such a constitution, the frequency of the vibrator 5 can be quickly controlled in a natural environment by a dissociating function of the light emitted from the device 1. Thus, the productivity of the vibrator 5 is improved and the vibrator 5 has no spurious vibration to improve its reliability.