To prevent the damage of soundproof and vibration-isolating functions by mounting a cushioning material with a recessed section, into which the head section of a bolt support leg screwed to a nut material fixed onto the rear of a floor pan is inserted, and a neck section covering the head section and having a small diameter.

A recessed section 11, into which the bolt head section 21 of a bolt support leg 20 screwed into a nut material 2 fixed onto the rear of a floor pan 1 is inserted, and a neck section 12 covering the head section 21 and having a small diameter are formed on a cushioning material 10 made of a rubber, and the head section 21 inserted into the recessed section 11 is covered with the neck section 12 and falling-off is prevented. The height of the head section 21 of the bolt support leg 20 is adjusted so that all head sections 21 are brought into contact on a building floor 5 at the beginning of the execution of works, but the central section of the floor pan 1 is warped up due to a change with time, the bolt support leg 20 is floated, the deformation of the floor pan 1 is returned when a man mounts on the floor pan 1, the building floor 5 is struck by the head sections 21, and an abnormal sound is generated, but the generation of the abnormal sound can be prevented by the cushioning material 10.