To provide a proper mixed mounting structure for a large span structure, which is very easy to work and construct without requiring experienced skill, thus to shorten a construction period and greatly reduce a construction cost.

Steel framed large beams 11 (12) continuously extended over a plural of spans are mounted in one direction between reinforced concrete columns 10. The ends of steel framed large beams 12 (11) continuously extended over a plural of spans mounted in the other direction crossing one direction are pin-jointed to the sides of the steel framed large beams 11 (12).