Method for manufacturing a guard rail in the form of a box profile (P') which has a rectangular cross-section and is extended longitudinally along an extension direction (x), with edges (K, K', K", K"') which run along the extension direction (x) and define the sides (S, S', S", S"') of the box profile (P'), comprising the steps: - supplying a flat sheet metal plate which is divided along the extension direction (x) into a first portion and a second portion, wherein the second portion is provided in the form of a free end portion of the plate, and the two portions (A, E) are connected to one another via a transition region, - tapering the second portion of the plate so that two outer margins (18, 19) of the plate running the along the extension direction (x) and lying opposite one another transversely to the extension direction (x) run up to one another in the transition region and have a shorter distance from one another transversely to the extension direction (x) in the second portion than in the first portion, and, - re-shaping the plate between a first and a second tool surface (W, W') to form at least one edge (K, K', K", K"') of the box profile (P') in such a way that the edges (K, K', K", K"') of the manufactured box profile (P') run parallel in the two portions (E, A) and run up to one another in the transition region, wherein the second portion of the manufactured box profile (P') has transversely to the extension direction (x) a cross-sectional surface area of the same cross-sectional contour as the first portion of the finished box profile (P'), but with a smaller cross-sectional surface area than the first portion of the finished box profile (P'), so that an angle of the second portion of the box profile (P') is produced which is designed in such a way that the guard rail (P') can be inserted along its extension direction (x) with the second portion into the non-angled end of an identically formed further guard rail (P') and can be connected there to the further guard rail (P') through fastening means, wherein the re-shaping is carried out by a device which has the following: - a first tool (30; 60) which forms a positive mould of at least one region of the manufactured box profile (P'), - a second tool (40; 70) with a socket (50; 80) which forms a corresponding negative mould of the at least one region of the manufactured box profile (P'), wherein the socket (50; 80) tapers in its cross-section along the extension direction (x), and - wherein the first tool (30; 60) is set up and provided to be inserted, with the interposition of the plate, into the socket (50; 80) in a direction of movement (z) oriented transversely to the extension direction (x) so that the two tools (30, 60; 40, 70) whilst re-shaping the plate are brought into positive-locking contact against each side of the plate. - supplying a flat sheet metal plate which is divided along the extension direction (x) into a first portion and a second portion, wherein the second portion is provided in the form of a free end portion of the plate, and the two portions (A, E) are connected to one another via a transition region, - tapering the second portion of the plate so that two outer margins (18, 19) of the plate running the along the extension direction (x) and lying opposite one another transversely to the extension direction (x) run up to one another in the transition region and have a shorter distance from one another transversely to the extension direction (x) in the second portion than in the first portion, and, - re-shaping the plate between a first and a second tool surface (W, W') to form at least one edge (K, K', K", K"') of the box profile (P') in such a way that the edges (K, K', K", K"') of the manufactured box profile (P') run parallel in the two portions (E, A) and run up to one another in the transition region, wherein the second portion of the manufactured box profile (P') has transversely to the extension direction (x) a cross-sectional surface area of the same cross-sectional contour as the first portion of the finished box profile (P'), but with a smaller cross-sectional surface area than the first portion of the finished box profile (P'), so that an angle of the second portion of the box profile (P') is produced which is designed in such a way that the guard rail (P') can be inserted along its extension direction (x) with the second portion into the non-angled end of an identically formed further guard rail (P') and can be connected there to the further guard rail (P') through fastening means, - a first tool (30; 60) which forms a positive mould of at least one region of the manufactured box profile (P'), - a second tool (40; 70) with a socket (50; 80) which forms a corresponding negative mould of the at least one region of the manufactured box profile (P'), wherein the socket (50; 80) tapers in its cross-section along the extension direction (x), and - wherein the first tool (30; 60) is set up and provided to be inserted, with the interposition of the plate, into the socket (50; 80) in a direction of movement (z) oriented transversely to the extension direction (x) so that the two tools (30, 60; 40, 70) whilst re-shaping the plate are brought into positive-locking contact against each side of the plate.