To dispense with a screw hole of a support body, facilitate fastening even in a narrow space, and prevent droppage of a nut body by composing the nut body at least of an assembly of a magnetic body, a screw hole body and a droppage preventive body linked thereto.

A nut body 1 is composed of a rectangular magnetic body 1A made of metal or rubber, a screw hole body 1B attached thereto, a base plate 1C integrated therewith, and a droppage preventive body 1D linked thereto by a wire 1d. A screw hole 1b of the screw hole body 1B is aligned concentrically with a screw body through-hole 2A formed on a specified position of a support body 2. The resultant body is attracted to the support body 2 by means of a magnet body IA, while the droppage preventive body 1D is engaged with the support body 2. A supported body 3 is abutted against a specified position of the support body 2. A screw body 4 is inserted into the screw body through- hole 3A and the screw body through-hole 2A and fastened thereto. The screw body 4 is screwed into the screw hole 1b to fasten the support body 2 to the supported body 3. It is thus possible to dispense with a screw hole of the support body, elongate the life, facilitate the fastening operation and prevent droppage of the nut body.