Abstract: A door impact beam, which is arranged in a door panel structure, comprises a beam body, arranged along the longitudinal direction of a door, and attachment portions arranged individually at two opposite ends of the beam body. The beam body is formed of a heat-treated hollow member steel. The attachment portions are individually fixed to the door panel structure. The beam body has a section in the form of a quadrilateral frame having four sides and four rounded corners. The outer radius of curvature R of each of the four corners is adjusted to a value such that the radius R falls within a range of 1.5 t.ltoreq.R.ltoreq.3.5 t, where t is the wall thickness of the hollow member.