To easily perform execution work by a dry system, and easily adjust a floor surface height by performing execution work of porch floor from metallic frames to be fixed above the ground surface and floor panels to be arranged on the frames.

Metallic frames 25 and footing rising parts 24 are fixed together by bolts through hole-in anchors. On the other hand, the metallic frames 25 and porch columns 2 are fixed together by connecting mutual L-shape anchors respectively arranged on the respective metallic frames 25 and the porch columns 2 by bolts. In this case, a floor panel 26 is composed of concrete boards 36 and finishing plates 37, and is fixed on the metallic frames 25. The concrete boards 36 are juxtaposed on the metallic frames 25 in an engaging condition of a projecting part and a recessed part, and these concrete boards 36 are fixed to square pipes of the metallic frames 25 by anchors.