PURPOSE: To contrive the facilitation of execution work and the improvement of noiseproof and vibro-isolating performance by providing a bag-shaped unit, which is filled with a liquid-state polymer composition, in one part of a strut of a floor plate and, after it is horizontally adjusted, hardening the liquid-state polymer composition.

CONSTITUTION: A bag-shaped unit 3, which consists of fiber reinforced polyester or the like having rigidity of certain degree, is provided in a strut 2 mounted to a floor plate l. Next a liquid-state polymer composition, mainly composed of hydroxyl group contained liquid-state diene system polymer or its hydride and a polyisocyanate compound, or a liquid-state elastic unit of urethane resin or the like is provided. Then the bag 3 is filled with the before described liquid state object, and it is hardened naturally or by heating after the floor 1 is horizontally adjusted. Thus, by eliminating the necessity for adjusting height of the strut one by one as in the past by a screw or the like, soundproof and vibro-isolating performance and durability can be improved while being possible to adjust horizontally and height of the floor plate.