A reinforcing brace excellent in productivity and cost performance is provided which can advantageously improve a rigidity of a floor panel without deteriorating aerodynamic performance. The reinforcing brace comprising a longitudinal press-formed product including a cylindrical section 12 located at a middle area in a longitudinal direction thereof and flat portions 44, 44 located at end areas in the longitudinal direction thereof. Further, an outer surface of the cylindrical section 12 is made as regulating surfaces 26, 32, 36 which reduce air resistance by regulating a flow of air passing under the vehicle body. Furthermore, a plurality of insertion holes 46 are positioned in the flat portions 44, 44 into which fastener members are inserted.