To firmly mount a floor material or wall by mounting a floor receiving metal fitting on at least a part of the longitudinal upper surface of a floor beam, and mounting a soft fireproof material around the floor beam under the floor receiving part of this floor receiving metal fitting to support the floor material.

A floor receiving metal fitting 20 is mounted on at least part of the longitudinal upper surface of a floor beam 11 consisting of mutually opposed channel steels. A soft fireproof material 19 is mounted around the floor beam 11 under the floor receiving part of this floor receiving metal fitting 20, a floor joist 22 is mounted on the floor receiving part of the floor receiving metal fitting 20, and a floor material 23 is mounted on the upper surface of the floor joist 22. Further, a joint floor material 26 is laid between the floor joists 22 of the floor receiving parts of the floor receiving metal fittings 20 mounted on the opposed floor beams 11 of mutually adjacent building units 10A, 10B. After the building units 10A, 10b are mounted, a rock wool receiving metal fitting 27 is laid between the side surfaces of the floor beams 11, rock wool 28 is filled therein, and the soft fireproof materials 19 are mutually connected by a connecting tool 29. Accordingly, the mounting property of the floor material can be improved.