To efficiently carry out an attaching/detaching work of a part to be tightened having a thread portion.

A part to be tightened which is urged and supported in the inside of a socket 14 can be easily and rapidly pushed out by a bamboo shoot spring in the inside of the socket by backwardly sliding the socket. The part to be tightened can be stably supported in the inside of the socket 14 without being dropped off by the bamboo shoot spring 22 urging an inner periphery of the socket 14 including a spherical body 16 and a tip end of the part to be tightened. Since a socket supporting portion 18 radially and pivotably supports the socket 14, even if the socket 14 is not accurately approached to the part to be tightened, an engagement of both members can be easily carried out. As a result, an attaching/detaching work can be efficiently carried out.