PROBLEM TO BE SOLVED: To make an edge part (head part) capable of mounting/demounting relating to a shank part and replace only a worn edge part so as to reduce labor for tool control and expense of a tool. SOLUTION: In one end part of a shank part 1, a clamp member insertion hole 5 is concentrically formed, and in a side part, a screw hole 13 connected to the clamp member insertion hole 5 is formed. In an edge part 7, a clamp member through hole 7a formed with one end side in a tip thick tapered surface 7b is formed. One end of a clamp member 6 is formed in a tip thick tapered large diametric part 6a corresponding to the tapered surface 7b of the clamp member through hole 7a, and in a side part, a notch 11 having a tilted side wall 11a is formed, penetrating the clamp member through hole 7a in the edge part 7, to be inserted in the clamp member insertion hole 5 in the shank part 1. Rounding work is applied to a tip end 8a of a screw 8 screwed to a screw hole 13, the tip end 8a is brought into contact with the wall surface 11a of the notch 11, the clamp member 6 is retracted to a side of the shank part 1.