PURPOSE: To improve the efficiency of construction work, and to ensure the strength of assembly.

CONSTITUTION: A plurality of columnar materials 3 constituted by vertically connecting a plurality unit columnar materials 31, 32, 33, 34 consisting of pipe bodies are installed in upright on a footing 1. The columnar materials 3 are used for constructing the columnar structures l formed by joining the columnar materials 3 through beam materials 4, backing strip materials 8 are fixed onto the internal surfaces of at least joining ends of the upper unit columnar materials 3 while first joint flanges 6a covering the joining ends of the lower unit columnar materials 31 are connected at the joining ends of the lower unit columnar materials 32, and flanges 6b arranged to the first joint flanges 6a at intervals are penetrated to the unit columnar materials 3 and formed as second joint flanges. Hole sections 6c are shaped to the first joint flanges 6a and the second joint flanges 6b, annular receiving sections 6as are formed to the first joint flanges 6a, the first joint flanges 6a and the second joint flanges 6b are projected and extended in the direction of the beam materials 4 to shape extended sections 6a1, and 6b1, and the extended sections 6a1 and 6b1 are joined mutually by webs 6d, thus forming joint sections 61.