To easily provide a light channel steel having large second moment of cross-section even with the same weight and the same profile dimension by constructing a flange part of laminated steel sheet and increasing its total thickness more than the thickness of a web part.

After executing the hemming fold-back working to both sides of a thin steel plate, the steel plate having the hemming fold-back part is bent on both sides to obtain a light channel steel having the cross-sectional shape in which a flange part has double, triple or more folds. A seat-dug hole is preferably formed in an outermost side steel plate of the flange to a part to which the light channel steel is joined. Other plate such as a steel plate, a rubber or the like is preferably interposed on the hemming fold-back part. Further, a folding groove is preferably formed in the web part and/or the flange part.