To improve absorption of energy in collision and to improve safety by making both flanges into cavity parts, integrally molding a web with the flange parts into H-type shape steel, and forming radius of curvature parts on both ends of both flanges and the connecting parts of the flanges and the web.

In a reinforcing material to be arranged in an automobile door to secure safety by absorbing energy in collision in relation to lateral collision of the automobile, both flanges 4, 4a formed into cavities 5, 5a and a web 6 are integrally molded into H-type shape steel 7. Eight radius of curvature parts R1 to R8 are formed on both ends of both flanges 4, 4a of the H-type shape steel 7 and the connecting part of the both flanges 4, 4a and the web 6, a recessed part is formed in the width direction of the H-type shape steel 7, and a function for restraining the sectional surface from being crushed is exhibited. Therefore, absorption of energy is reliably restrained from being lowered caused by flattening of the sectional surface and buckling deformation in the bending direction in relation to loading even if the plate thickness of the reinforcing material is thinned.