PURPOSE: To remove a cutter from an adaptor simply by a method wherein a tightening bolt is loosened slightly and the cutter is pivoted by a predetermined angle.

CONSTITUTION: A notched portion 29 of a cutter 20 is aligned with a protruded portion 34 of an intermediate member 23 and the cutter 20 is forced toward adaptor 4 side. Thereafter, the cutter 20 is turned by a predetermined angle and a tightening bolt 22 is tightened, thereby tightening the cutter 20 to the adaptor 4. When the cutter 20 is removed from the adaptor 4, and tightening bolt 22 is loosened slightly firstly, then, the cutter 20 is turned reversely by a predetermined angle to remove the cutter 20.