Abstract: A track building machine (34) for the renewal of tracks, essentially comprising a machine frame (1), supported on rail mountings (2, 3), having a work aggregate (38) exhibiting devices (5, 6, 7) for preparing a ballast bed, for lifting out old ties (8) and for laying new ties (9), and additionally comprising devices (35, 36, 10, 11, 12) for transporting the old and new ties (8, 9) and for raising, guiding and stretching apart old rails (13). For the support of the rail mounting (3) in working deployment, which rail mounting is disposed directly in front of the work aggregate (38) in the direction of working, a slide mechanism (18) is provided, which is rollable on the old ties (8). The work aggregate (38) for lifting out the old and laying the new ties (8, 9), outside a section limited by the rail mountings (2, 3) connected to the machine frame (1), is fastened on an extension arm (4) prolonging the machine frame (1).