To construct a floor vibration proof system into a simple and lightweight one by damping the vibration of the center of a floor slab using a damping material based on the fact that the vertical vibration of a floor face consists mainly of large vibration of the center of the floor slab.

A restraint member 10 is placed above a floor slab 11 in such a way as to pass through the center of the floor slab 11. The restraint member 10 has a liner plate 15 of a predetermined thickness which is welded to the lower surface of a lower flange 10a at each end of the restraint member 10, and the restraint member 10 is secured to the periphery of the floor slab 11 via the liner plate 15. A pair of holding members 17 are provided which are located on both sides of the restraint member 10 and secured to the center of the floor slab 11. A pressing plate 22 is secured to the end face of the arm part 19 of the holding member 17, and a receiving plate 24 is secured to each side of a web 10a at the center of the restraint member 10. A viscoelastic material 24 is sandwiched between the pressing plate 22 and the receiving plate 24.