To firmly assemble a steel construction.

In order to join two reinforcing steel materials of a steel construction, while the first slide-restraining working surface having one or a plurality of crests and grooves disposed around a coupling hole is concentrically formed on one joined surface of the reinforcing steel material, the second slide- restraining working surface having crests and grooves fitted to be meshed with crests and grooves of the first slide-restraining working surface is formed on the other joined surfaces of the reinforcing steel material. The two reinforcing steel materials can be tightened so as to mesh the first and the second slide-restraining working surfaces each other by a coupling member running through the coupling hole.