To reduce labor by site work, and combine a floor, a column and roof eaves with each other by systematization by forming a unit whose completion degree is enhanced by factory production.

A unitized porch column 2, a porch floor 3, porch roof eaves 4 and a balcony constituting member 57 are produced in a factory, and these are assembled at a job site. In this case, since the porch floor 3 is respectively fixed to a lower part of the porch column 2 and a footing rising part of a porch entrance, it is arranged in a position above the ground surface, and influence is wholly eliminated on a condition of an execution work place. The porch floor 3 is composed of a preformed concrete board and a finishing plate, and execution work is simplified by assembling it at a job site, and a dry system can be realized The porch roof eaves 4 are formed as an integral structure out of a metallic plate such as aliminium separately from a building 1, and execution work is facilitated, and the balcony constituting member 57 is combined with an upper part. Therefore, a balcony having a united feeling with the porch column 2 can be formed.