PURPOSE: To certainly avoid the trouble that the cutter of a cutting tool is broken into a product, by forming a substitution breakage part in the holding part of the cutting tool.

CONSTITUTION: An intermediate holding metal ware 5 firmly holds the shank part 16 of a cutting tool 1, and the basic edge part 5b is firmly fixed onto a tool holding fixture 2, and installed onto the spindle 3 of the machine tool. The intermediate holding metal ware 5 has a substitution breakage part 5c recessed at the center part, and the torsion resistance strength is set to sufficiently endure the ordinary work of a cutter part 1a and set weaker than the torsional breakage force of the cutting part 1a. Further, an air flow thin hole 6 is formed, penetrating through the tool holding device 2 and the spindle 3 to the vicinity of the center of the sectional surface of the substitution breakage part 5c of the cutting tool 1, and since an air pressure 8 is applied, the destruction of the breakage part can be easily detected by an air leak detector 7. Therefore, the trouble that the cutter of the cutting tool is broken into a product can be certainly prevented.