To provide a screw driving tool by which tightening or removing screw members such as a bolt, a nut or the like can be justly performed without co-rotation of these members only by a handle operation.

This tool is equipped with a main part A in which primary back stop mechanism 2 is installed on the circumference of a main rotary body 1 on which a socket 8 fitting on screw members is formed, and with an auxiliary part B having a handle 6 by which secondary back stop mechanism 5 is operated, after such an auxiliary rotary body 4 that the secondary back stop mechanism 5 is installed on its circumference is engaged with the main rotary body 1. Hereby, screw members fitted to the socket 8 can be rotated in one direction by a handle operation.