PURPOSE: To vibrate a vibration transmitting member at large amplitude without applying unreasonable stress to said member when the vibration transmitting member is subjected to ultrasonic vibration by a magnetostriction vibrator, by forming the magnetostriction vibrator so as to have a structure generating nonuniform vibration.

CONSTITUTION: The magnetostriction member 8 of a magnetostriction vibrator 7 is formed so that the magnetostriction quantity thereof becomes nonuniform. Therefore, the quantity of strain generated by applying high frequency voltage to the magnetostriction vibrator 7 also becomes nonuniform to generate lateral deflection and, as a result, the leading end of a vibration transmitting member 5 is vibrated not only in the axial direction but also in the longitudinal direction thereof. Since the leading end of the vibration transmitting member 5 can be vibrated at sufficiently large amplitude by the longitudinal and lateral vibrations, the emulsification of tissue 14 can be performed efficiently and certainly. Since the amplitude of the vibration transmitting member 5 is made large by lateral vibration, it is unnecessary to apply large stress to the root of the vibration transmitting member 5.