PURPOSE: To prevent over-tightening a screw member due to the impact use of a rotary tool, to easily detach the screw member, to obtain large tightening force and powerful loosening force even by a small rotational input, and to enable the powerful tightening and the easy loosening even by the direct manual operation.

CONSTITUTION: A screw member comprises a flange ring 12, operation rings 13 and 12, a return screw ring 14 which is screwed to an outer circumferential part of the screw member by regulating the screw feed, a screw feed ring 15 to transmit the screw feed to the flange ring 12, and a holding ring 16 to permit the revolution of the screw feed ring 15. The screw feed ring 15 is screw-fed by the revolution of the screw feed ring 15, and the flange ring 12 is pressed by the torque-up force in the thrust direction to fix a work to be fitted.