PURPOSE: To fix a nut seated in a groove to prevent the nut from slipping off without using an adhesive material or a fixing O-ring in a bolt-fastening structure for fastening structures with each other.

CONSTITUTION: A nut 10 is seated in a lateral groove 4b of an insulating frame 1 as a structure in contact with the groove bottom in order for the nut to be screwed on a screw of the body part of a bolt 6 which is passed through a bolt hole 7 of a supporting body 3 as a structure to be inserted into a vertical groove 4a. Then, a presser plate 11 made of a rectangular elastic plate made slightly larger than the groove width of the lateral groove 4b is inserted into the lateral groove 4b to be deformed and deflected to produce spring-inertia in itself. The presser plate 11, in which spring-inertia is produced, is pressed against the side face of the seated nut 10 to prevent the nut 10 from falling off and to fix the nut.