To obtain a fixed structure of a cartridge with a high speed limit for the rotation of a tool main body.

A recessed groove 13 opened on a tip surface and outer periphery surface is extended in nearly parallel with a rotary axis and formed in the periphery direction at a prescribed interval on the outer periphery of the tip of a nearly cylindrical tool main body 12. This recessed groove 13 is formed so that the inner wall 13a extended along the insertion direction of a cartridge 14 is slanted for the diameter direction and thereby, the opening of the recessed groove 13 to the outer periphery surface is constituted so as to become narrow gradually heading for the outside of the diameter direction. It is favorable that this slant angle α is set by 20°.