To rationalize and improve efficiency of beam construction by mounting a reinforcing steel plate having a U-shaped cross section to the inside/outside face or each of them in a main body pat made of a steel folded plate with a U-shaped cross section.

This placing mold 11 is constructed of the main body part 12 made of the steel folded part and provided with U-shaped cross section and inside and outside reinforcing steel plates 13, 14 mounted on the inside and outside faces of the main body part 12. The inside reinforcing steel plate 13 is formed of a steel plate, which is previously bent into a shape with a U-shaped cross section so that its shape and dimension are set suitably for covering the whole of the inside face of the main body part 12, and mounted on the inside of the main body part 12. The outside reinforcing steel plate 14 is mounted on the whole outside face of the main body part 12 in the similar way. The placing mold 11 is formed into a hollow structure constructed of layers of three steel plates as a whole, and its strength, especially overall bending rigidity is greatly increased. In this way, a concrete placing load can be supported by the placing mold 11 itself, so that timbering in the intermediate part can be dispensed with, and working efficiency of beam construction can be greatly improved.