PURPOSE: To prevent a mounting face from being injured when a special screw having a screw groove on the end face of a polygonal screw head by putting a cylindrical body in the condition of being pressed against the mounting face so as not to contactedly rotate at contacting the extreme end of the cylindrical body with the mounting face.

CONSTITUTION: When the screw head part 3 of a screw 1 is fitted in the nut bit part 22 of the cylindrical body 13 of a driver bit 11, the extreme end of a male screw part 2 is brought in contact with the fitting hole 7 of a mounting face 6, and the driver main body is rotated, a shaft body 12 and the cylindrical body 13 fitted to this are rotated, and the male screw part 2 is screwed in. By this screw-in, the extreme end of the cylindrical body 13 is brought into contact with the mounting face 6, in addition when torque is applied on the shaft body 12 while pressing the driver main body against a spring 27, the screw head part 2 is detached from the nut bit part 22, the shaft body 12 is moved on the face 6 side, the fitted part of the shaft body 12 is detached, then a screw bit part 16 is engaged with the screw groove of the screw head part 3, and the cylindrical body 13 is not rotated and the shaft body 12 is only rotated so as to thread-mount the screw 1.