To contrive improvement of heat insulation by fixing a heat insulation bed panel between a steel frame beam and floor material and disposing heat insulation material at the indoor side of the web of the steel frame beam.

A plurality of runner fixing fittings 2 are attached to the lower flange of a steel frame beam H at intervals in a case where a heat insulation inner wall bed 1 is constructed. Next, a runner 3 is fixed over each fitting 2, and a plurality of fixing fittings 4 are fixed on floor material F at intervals. A heat insulation inner wall bed panel 5 is constructed on the floor material F separated from an outer wall W at a constant distance with the runner 3 and the fitting 4. Furthermore, heat insulation material 61 is disposed at the indoor side of the beam H, and heat insulation material 62 is disposed between the lower flange of the beam H and the runner 3. Thereby since the outer wall W side and the indoor side can be prevented from heat exchanging through a space and a ceiling formed between the lower flange of the beam H and the runner 3, higher heat insulation performance can be secured.