PURPOSE: To reduce a production cost by making the deformed material of the sectional shape combining plural pieces of the necessary section and then by cutting in longitudinal direction after a drawing work.

CONSTITUTION: The deformed material of a long size having the sectional shape combining two pieces of the section of the necessary deformed material 10 is made. A deformed material 20 is made corresponding to the up and down and right and left lines and the specific gravity position is positioned at almost the center of the outer shape of the section. A long sized deformed material 20 is subjected to a drawing work with a correct dimensional accuracy. It is then cut in longitudinal direction along a point chain line (a) and the deformed material 10 having the necessary sectional shape is obtd. with high accuracy. High accuracy is secured respectively for the inclined face 16 of the deformed material 10 by the drawing work and for the upper face 14 of the wing 12 by the work after cutting. The conventional cutting work for the wall thickness part is made disused and a simple cutting work is required only, so the production cost is remarkably reduced.