PURPOSE: To cut the body to be cut of a bulky ground while repressing the generation of a wrinkle, by supporting a round tooth rotatable at the position eccentric to the rear part in the cutting progressing direction with a rotating shaft on the lower end of this rotating shaft and also connecting this round tooth to a rotation driving part.

CONSTITUTION: A round tooth 9 is ascended, an YX table is moved and the center of the round tooth 9 is arranged on the point D' located on the extension line which is extrapolated in the reverse direction from a point D to the curve connecting the point D and a point E. In succession, the moving means of a rotating shaft 4 is operated to a descent side, the round tooth 9 is descended via the rotating shaft 4, the round tooth 9 is made in a free rotating state, the XY table is moved and the round tooth 9 center is moved to the point D from the point D'. The round tooth 9 is thus fitted at the position eccentric to the rear part for the cutting progressing direction to the rotating shaft 4 and yet it is made rotatable freely around the rotating shaft 4, so the tooth angle coincides with the round tooth in the shape of the side DE to be cut while moving to the point D from the point D'.