PURPOSE: To provide a tool capable of driving and removing even a stud having a large diameter incapable of grasping in a work piece without damaging the same.

CONSTITUTION: A stud driver comprises a main ring 12 having a shaft hole 16 adjacent to a driving adaptor 10 at its one end and having a taper surface 18 on the other surface, a core 17 capable of limiting its axial motion and rotating motion to the main ring 12 and located in the main ring 12, and at least five rollers 27 between the taper surface and the core 17. An axially extended cam surface 30 is formed on the taper surface for locking the main ring 12 and a stud when the core 17 is rotated relative to the main ring 12. A ratio of the cross-sectional areas of the stud to one roller is about 5:1. A recessed 66 for respectively accepting each roller 27 is formed on each cam surface, so that a screw thread can be prevented from being damaged by the roller 27 by putting the roller 27 in the recessed, for example, when the roller 27 passes through a large diameter part of the stud having the screw thread.