SCREW FASTENING TOOL WITH MARKING FUNCTION

PROBLEM TO BE SOLVED: To provide a screw fastening tool capable of performing marking to a screw head surely after detecting that screw fastening torque reached to a predetermined value.SOLUTION: An impact wrench 1 has a socket part 10 at a tip end of an impact wrench body 2. The socket part 10 is configured so that a socket body part 11 and a socket tip end part 20 are separated through a coupling metal fitting 17 and a rubber band 18 configured so that they can be locked. When fastening torque reaches to a predetermined value, a first air circuit 30B for performing rotation driving of the socket part 10 and a second air circuit 30 configured individually are operated and marking is performed by moving a marking part 13 toward a screw head.