portion 52 at which the tap collet 50 and the tapper body 20 are overlapped the locking member 70 includes a male screw portion 72 and a locking shaft portion 74 formed on a front end side of the male screw portion 72 and inserted to the through holes 28 and 56 a peripheral face of the locking shaft portion 74 is formed with a plurality of first recessed portions 76 in a groove like shape continuous in a peripheral direction to be spaced apart from each other by predetermined intervals thereamong in an axial direction of the locking shaft portion 74 and the respective first recessed portions 76 are arranged with elastic members 78 to project from the locking shaft portion 74 to an outer side the elastic member 78 is a ring like member formed by a synthetic resin having an elasticity of nylon or the like or rubber and is removably arranged to the locking member 70 the locking member 70 is fixed to the tapper body 20 by screwing the male screw portion 72 with a female screw portion 32 provided at an inner peripheral face of the through hole 28 in a state of inserting the locking shaft portion 74 to the through hole 28 56 thereby the tap collet 50 is engaged with the locking member 70 in a state of interposing the elastic members 78 on both sides in an axial direction of the tap collet 50 indicated by an arrow notation x and is unrotatably fixed to the tapper body 20 further an end face 52 a of the shaft portion 52 opposed to a bottom face 26 a of the attaching hollow portion 26 is arranged with a plurality.