To provide a hollow extrusion structured light and with rigidity in a joining part increased and provide a structure for a railroad car formed from the hollow extrusion.

The hollow extrusion 1 is embodied in a truss construction such that a plurality of swash plates 13 are set over between an oversurface plate 11 and an undersurface plate 12 and the section in the width direction is shaped triangle by the oversurface plate 11, undersurface plate 12, and the swash plates 13, wherein the intersection p3 of the center lines L of adjoining swash plates 13 lies on the oversurface plate 11 or the undersurface plate 12.