PURPOSE: To cut a workpiece precisely in a short time by a method wherein a vertical motion device is so constructed that the workpiece together with a rotary driver are vertically moved, and the workpiece is pushed against a blade.

CONSTITUTION: When a motor 54 of a rotary driver 14 is operated, a rotary shaft component 72, a base glass 73, and a workpiece 80 are integrally rotated. When a driving motor is operated under a state a blade 78 is fitted under a sliding frame, the blade 78 is reciprocated, and at the same time a polishing feed pump is operated to start cutting of the workpiece 80. In that case the rotary driver 14 is gradually pushed up with a vertical motion device, and the workpiece 80 is cut under a state it is lightly pushed against the blade. That is, though a cutting edge face 78m is formed by an outer peripheral face of the workpiece 80 and a working face of the blade 78 at start of working, a diameter size of a cutting part decreases as the working advances. At the point of time when the workpiece 80a is obtained, the cutting edge face 78 comes to be moved right to the cutting edge face 78n.