To obtain a welded structure, in which a high precision hollow rectangular tubes are simply and easily assembled, by notching a diameter equivalent part of a hollow rectangular tube or forming a V shaped notched part with using a colmuar die, bending the notched part and welding a bent part.

A hollow rectangular tube P is cut to a prescribed length for required dimension beforehand, a cut opening part is formed to the tube side face of hollow rectangular tube P. Half of cross section shape is notched in the longitudinal direction of hollow rectangular tube P at a fixed interval, further, the diameter equivalent part of hollow rectangular tube P is notched, a grooved notch part is formed. The grooved notch part of desired shape is formed to the hollow rectangular tube P with using a columnar die, a V shaped notched part of desired angle is formed to the hollow rectangular tube P having grooved notch part, further, the notched part of hollow rectangular tube P having notched part is bent, the bent part T is welded, a desired product of hollow rectangular tube P is assembled.