PURPOSE: To improve the revolving of an abrasive grain and to quicken the processing time by providing means which strikes a wire when a monocrystal ball is cut by a wire.

CONSTITUTION: A LiTaO3 monocrystal 11 is rotated to the right and left at the speed of a mean 10rpm, with the azimuth at 30° initially. The LiTaO3 monocrystal 11 is then moved in the vertical upper part direction A while rotating it, and sliced by a wire 3. At this time, the monocrystal 11 is sliced while tapping the wire 3 lightly by key boards 9a, 9b, when the speed of the wire 3 becomes zero. The interval of the key boards 9a, 9b is widened in the horizontal direction according to the processing being progressed, it is made in a constant interval, after the center of the LiTaO3 monocrystal 11 being sliced. The azimuth of this LiTaO3 monocrystal 11 is made smaller according to the progress of the working, and the rotation is stopped, when the half of the cut section reaches a glass base 15.