Automobile strength member, particularly side impact beam

An automobile strength member, having a cross-sectional shape giving a high bending repulsion at the beginning of impact and able to reduce the production cost and lighten the weight and achieve a greater improvement in safety and a reduction of cost of an automobile, that is, an automobile strength member comprised of a rectangular steel tube with a square cross-section, simultaneously satisfying the following relations (1) to (3), and having a strength of at least 690 MPa in terms of tensile strength: R 1 ‰1.5t t R ‰¥1.1t R 1 �¢ ‰¥R 2 where, t: thickness of side (mm) t R : thickness of corner (mm) R 1 : outside corner R (mm) R 2 : inside corner R (mm) €ƒ€ƒ€ƒwhere both a maximum value and minimum value of hardness at a cross-section of the rectangular steel tube are in the range of within ±30% of the average value of the entire cross-section.