Abstract: A rolling-stock underframe construction comprising longitudinal side sills, end sills connecting opposite longitudinal ends of one side sills to opposite longitudinal ends of the other side sill, body bolsters respectively disposed at positions corresponding to trucks, and center sills extending between the end sills and the corresponding body bolsters in parallel to the side sills; and a floor member fixedly disposed in an area defined by the side sills and the end sills. The floor member comprises an upper plate forming, a lower plate forming, and a corrugated plate disposed between the upper plate and lower plate. The corrugated plate includes an alternate arrangement of ridges and longitudinal furrows and is joined to both the upper and lower plate.