PURPOSE: To enhance the efficiency of construction by a method in which floor panels pivotally attached with columns in a fallen state are carried to a construction site, the columns are turned and fixed to the floor panels at right angle, and these are attached to the lower edge of the opening of a building.

CONSTITUTION: Columns 5 are rotatably attached through a rotary shaft 4 to the end of a floor panel 3, and the floor panels 3 are carried to a construction site under a condition that the columns 5 are fallen down. The columns 5 are turned and fixed to the floor panel 3 at right angle by bolts. The floor panels 3 are attached to the lower edge of the outlet opening of balcony of a housing unit. The quality of the balcony can be raised due to productibility in factory, and these parts can also be safely, easily, and quickly carried and constructed.