PURPOSE: To certainly and repidly attach and detach a hole processing cylinder in a large caliber hole processing tool wherein the hole processing cylinder is held around a center drill.

CONSTITUTION: A tool shaft body 2 having a center drill 3 and a cylinder holder 20 holding a hole processing cylinder 10 are fixed by screw fitting. The surrounding piece 47 protruding toward the boss part 22 of the cylinder holder 20 is provided to a taper disc 40 forcibly expanding the expanding and contracting wheel part 24 of the cylinder holder 20 to fix the hole processing cylinder 10 and a nut member 30 is threaded with the surrounding piece 47 to draw the surrounding piece 47 to the expanding and contracting wheel part 24. Since the tool shaft body 2 and the taper disc 40 are not directly subjected to screw fitting, the tool shaft body is not abnormally clamped at the time of use.