To realize excellent impact energy absorptivity by disposing a partition plate in such a way that cross-sectional areas of two spaces formed by the partition plate satisfy a specific expression in a beam-like steel structural member with at least-two outer shell parts jointed and with the partition plate disposed in closed cross section.

The layout position of a partition plate 2 is so set that cross-sectional areas A1, A2 of two spaces formed by partitioning closed cross section formed by outer shell parts 1, by the parition plate 2 satisfy the relation expressed by an expression (A2≤A3≤2A2). Tensile strength TS and thickness (t) of the partition plate 2 to the tensile strength TS0 and thickness t0 of the outer shell parts 1 is to be in a range satisfying expressions (0.3≤t≤0.6*t0 and 0.1≤TS*t0)≤0.3). A steel sheet member with the partition plate can therefore improve axial crush absorbing energy and maximum bending load considerably without causing large weight increase so as to heighten the collision safety of an automobile.