PURPOSE: To improve the execution workability and reduce the cost by providing in line a plurality of flat plate-shaped protrusions, having a fold part, in the lengthwise direction of an upper part runner and inserting these protrusions into a hollow hole in a panel to support its upper part.

CONSTITUTION: Nonflammable panels 6, 6, having at least one hollow hole- provided vertical rib 6b, 6b in the reverse side or having at least one longitudinal directional hollow hole 6a, 6a in the panel unit are supported by an upper part runner 4 and lower part runners 7, 7. In the case of this method of construction, a plurality of flat plate-shaped protrusions 4b, 4b having fold parts 4a, 4a, are provided in line in the lengthwise direction of the upper part runner 4 and inserted into the hollow holes 6a, 6a of the panels 6, 6 to support an upper part thereof. Thus, eliminating the necessity for work of cutting or the like in an upper surface of the panels 6, 6, while cutting of the panels 6, 6 in a work spot can be facilitated.