In recent years, from the viewpoint of protecting an occupant, the safety standard against the side collision of an automobile have been augmented, and the automotive door is required to exert the side collision performance sufficiently. In order to protect the occupant from the side collision, it is important to reduce the intrusion quantity of a colliding vehicle into the door part and to inhibit deformation of the door toward inside the cabin. In the side collision, the space for absorbing the collision energy is small compared with that in the collision of the front side and rear side. Against such collision, conventionally, a door beam was disposed inside the door along the vehicle traveling direction and deformation of the door toward inside the cabin was inhibited.
At present, a door beam of high tensile steel pipe and pressed material (Patent Document 1) or an aluminum extruded shape (Patent Document 2) has been developed and used. In general, for these door beams, one with a linear shape without a curve is used. In the Patent Document 3, a bending work method is described wherein a dent is not caused on an outside wall in bending in bending work of an extruded shape. Also, in the Patent Document 4, an embodiment is described wherein a door beam of a hollow body having a partitioning wall with a predetermined range being quenched is arranged in a direction oblique to a door.    Patent Document 1: Gazette of the Japanese Unexamined Patent Publication No. H8-216684    Patent Document 2: Gazette of the Japanese Unexamined Patent Publication No. H11-264044    Patent Document 3: Gazette of the Japanese Unexamined Patent Publication No. 2001-71038    Patent Document 4: Gazette of the Japanese Unexamined Patent Publication No. 2001-287608