PURPOSE: To perform easily and efficiently plane finishing treatment in a joint part in the stage of manufacturing a steel segment by welding a steel plate by packing a caulking material having excellent adhesiveness in the gap in a welding and joining part in place of performing caulking welding.

CONSTITUTION: Welding of a surface finished main beam 1 and a joint plate 2 in the stage of manufacturing a steel segment is accomplished by subjecting both members 1, 2 to normal welding A from the inside surface side then applying a caulking material C which is prepd. by mixing a resin having ductility and metallic powder such as iron powder at a ratio of 3:2 and mixing further an adequate amt. of the adhesive agent and has excellent adhesiveness and cold curability on the outside of the joining part of both members 1, 2 in order to form the joining part into a sure watertight construction. When the material C cures, the excess build-up part of the material C and the rough surface 2a of the plate 2 are simultaneously cut and ground, whereby the surface 1a of the beam 1 and the end part of the plate 2 are finished to the same plane.