PURPOSE: To make it possible to simplify work in a construction site and, at the same time, to prevent face members from damage in the case of mounting.

CONSTITUTION: Fire members 11A and 11B as first face members arranged lengthwise of a column 12 and a beam 13 as a flat part of a frame 10 are mounted to the columm 12 and beam 13. Fire members 11C and 11D as second face members arranged along structural uneven steps caused by a joint 14 as a flat part of the frame 10 and uneven parts caused by welding are mounted to the fire members 11A and 11B, and the fire members 11C and 11D are placed at a specific interval so that they are not contacted with the column 12 and beam 13. Accordingly, in the case the fire members 11C and 11D are mounted, troublesome work such as nailing work or inconveniences such as cracks occurring in the fire members 11C and 11D can be dissolved.