PURPOSE: To effectively utilize lifting capacity of a large crane by using a temporary installed frame, to ensure safety during work, and to remarkably shorten working time.

CONSTITUTION: Columns 1 and large beams 2 are erected on a foundation and meanwhile, a plurality of small beams 3 are placed on a mounting bed 17 of a temporary installed frame 10. After the temporary installed frame 10 in such a state that the small beams 3 are mounted is lifted by a tower crane and temporarily placed on erected large beams 2, the small beams 3 on the mounting bed 17 are caused to span between the large beams 2 by means of a girder 15 and a hoist crane 16.