PURPOSE: To facilitate the adjustment of fixing a grindstone in a range from fine working and strong slicing by causing the forward end of the grindstone secured to a booster located at the center position to be subjected to maximum radial expanding oscillation by ultrasonic oscillation of a converter at the rear end of a spindle.

CONSTITUTION: A converter 2 producing swinging oscillation waves is attached on the rear end part of a shaft which is directly coupled to a drive motor M so as to be rotated at a high speed, and a booster 3 provided with a holder for clamping and fixing a disc-shape grindstone 4 is attached on the center part of the shaft so as to form a spindle 1. The frequency range of an electrostrictive element production swinging oscillation waves in the converter 2 is set to be 15W45kHz, and the converter 2 and the booster 3 are adjusted in combination in accordance with a high speed rotation of the grindstone 4 in such a way that oscillation waves are transmitted to the forward end of the grindstone 4. Housing covers 5, 5' rotatably supports and covers both sides parts of the spindle 1 in its entirety excepting the part in the vicinity of the grindstone 4 extending orthogonal to the spindle 4.