To improve working efficiency by preventing slip off of a screw, and by preventing incline of a screw top end with a simple method.

The screw part 3a of a screw main body 3 is screwed in the penetrating hole 1a of a cover 1 after a spring 4 is inserted to a neck bottom part 3b. When the neck bottom part 3b of the screw main body 3 is out from the penetrating hole 1a, the screw part 3a is in a free condition, the screw head part 3c of the screw main body 3 is energized in a direction reverse to the installing direction of the screw part 3a by tension of the spring 4, and the center shaft of the screw main body 3 is held in substantially parallel with the center shaft of the screw hole 2a.