The invention is to provide a method and a device, etc. for molding tubes, free from any fear of the web being broken, which do not generate any wrinkle on a web when molding a plate-like web to rectangular parallelpiped packaging containers via a tubular web. In a tube molding method of the invention for molding a plate-like web to a tubular web while transferring the former along the roller surface formed by a plurality of rollers 11 through 13 of the molding roller 4, a roller supporting plate 16 is turned by a tightening member 29 while being position-regulated by a roller 25 attached to the roller attaching arm 23 so that web is transferred on the basis of the hypothetical center axis line (Point X) of the tubular web, which is formed by the roller surface constituted by the rollers 11 through 13, wherein the web in the lengthwise direction can be accurately transferred so that the same web takes a predetermined orientation of the rollers 11 through 13. As a result, it is possible to produce a high molding accuracy, for which the creasing lines of web in the lengthwise direction are made coincident with ridges of square-post-like web in its lengthwise direction when molding the square-post-like web from the tubular web.