To provide a driving device for an ultrasonic vibrator which always drives the ultrasonic vibrator by its resonance frequency and easily copes with ultrasonic treating apparatuses for medical operation, ultrasonic fusion, or the like, which have been diversified.

From a voltage signal V1 of an ultrasonic vibrator 1 and a signal amplified of a voltage signal V2 of a capacitor 10a for correction by means of an amplifier 20, a resonance circuit phase signal Vf2 is calculated by means of an arithmetic tool 21 for phase synthesis. Ratio A of amplification of the amplifier 20 is adjusted by means of an amplification ratio adjusting circuit 22 based on an oscillating frequency fo. The oscillating frequency fo is adjusted by means of a PLL control circuit 30 using an applied voltage phase signal Vf1 corresponding to the voltage signal V1 and the resonance circuit phase signal Vf2. The ultrasonic vibrator 1 is thereby always surely driven by a resonance frequency.