To prevent a nut from being drawn out to disappointment by screwing a first cover in the end part protruded from a nut screwed to a bolt fastening a member, putting a second cover covering the first cover and the nut over them, and connecting both covers together by means of a connecting means.

For preventing the dawing-out of a nut 13 screwed to an external thread 11 extending through first and second members 17, 19 tightly touching each other, a first cover 21 is installed to a tip part 11a protruded from the external thread 11 in the nut 13 by engaging an internal thread part 23 formed in the inner circumference so that an opening edge part 27 of the first cover 21 is brought into contact with one end 13b of the nut 13. A second cover 29 is arranged so as to cover the nut 13 and the first cover 21, and the second cover 29 is connected to the first cover 21 by means of a connecting member 39 constructed of a rod type member provided with a leg part 41 and a head part 43. In this process, the leg part 41 of the connecting member 39 is forcibly inserted into an opening formed in the bottom 25 of the first cover 21 so as to close it.