To secure wall surface rigidity of a body skeleton member making a closed cross section and extending in the longitudinal direction and to lighten it.

It is a body skeleton member (side sil) 10 of a vehicle consisting of two plate members 12 and 14 connected to each other by flange members 12A, 12B, 14A, 14B along the longitudinal direction to make a flat cross section. The inside plate member 12 is formed of a hollow plate member extrusion molded having a hollow space 18 inside. Two plate parts 20 and 22 of the hollow plate member are integrally connected to each other by a plural number of ribs 24, and the ribs 24 are provided adjacent to each other on curved parts 12C and 12D. Additionally, the inside plate member 12 has a portion (connecting part) 26 on which the two plate members 20 and 22 are crimped and processed on each other, and the ribs 24 on this portion are moved by plastic deformation to the inside of a recessed part previously formed on an inner surface of the plate part in their neighbourhood.