PURPOSE: To achieve beautiful finish with good cutting quality by reducing cutting resistance and to easily carve even a character or line having narrow width by forming an edge body having an almost semicircular cross section and a taper shape by removing a half along a flat surface containing a rotary axis on the leading end side thereof and forming an end edge part on one side into an edge part.

CONSTITUTION: For example, an edge body has a needle shape wherein the diameter shown by D is 3.175mm and the total length shown by L1 is 110mm and, for example, the outer peripheral surface thereof is formed into a taper conical shape over the length of 12mm shown by L2 from the leading end thereof and the edge body is notched along a flat surface containing a rotary axis 12 over the length of 16mm shown by L3 from the leading end thereof to form a notch part 13. Therefore, the cross-sectional shape of the edge body in the vicinity of the leading end thereof becomes almost semicircular and the end edge part on one side thereof is ground to form an edge part 15. In order to hold strength so as to prevent the breakage of the edge body 10, for example, the angle of the leading end part of the edge body 10 is made large over length of 0.05mm or less. The edge body 10 is passed through a holder 20 to be fixed by two screws 21 and rotated along with the holder 20 to cut a seal material 23.