To improve abrasion resistance of a bush, minimize regrinding and replacement frequency, facilitate attachment and detachment of the bush, and improve runout accuracy of a bush inside diameter to a tool body at a low cost.

A bush 3 for inserting a hole processing tool into the front end of the tool body 1 whose rotation is driven around its axis line is inserted coaxially with the axial line, and is fixed so as to be detachable by a clamping screw 14. A covering layer with abrasion resistance is formed at the inner surface of the bush 3. A bush accommodating hole 11 for inserting the bush 3 into the tool body 1 is constituted of supporting parts 11a, 11b formed by processing the inside diameter with high accuracy so as to be fitted to the bush 3 respectively at a part of the inner surfaces on its front end side and rear end side, and an enlarged diameter part 11c formed into a larger diameter than those of the supporting parts 11a, 11b.