PURPOSE: To provide a nut fitting jig with a simple structure and a method capable of easily conducting the fitting work of a nut by using this.

CONSTITUTION: A jig 11 has an attracting part 13 of a magnet for attracting the jig near nut fitting position 12, an arm 14 in which one and 14A is fixed to the attracting part 13 and the other and 14B is extended to the nut fitting position 12, and a male screw part 15 cut in the other end part of the arm 14. The nut fitting method using this jig 11 comprises the process of forming a hole part 18 on the beam 16 of the nut fitting position 12, the process of attracting the jig 11 near the nut fitting position 12 so that the nut 17 is held in the hole part 18 in the state where the nut 17 is spirally fitted to the male screw part 15 of the jig 11, and the process of welding the nut 17 to the beam 16 of the hole part 18.