Abstract: Safety belt roll-up device having a housing and a one-piece belt carrier. The housing has a base plate with two side walls extending from the base plate. At least one of the two side walls can be set at an angle and bent into a position in which both side walls are parallel. Each side wall has an opening through which a free end of the one-piece belt carrier extends. The one-piece belt carrier is in the form of a single piece including a belt shaft and a belt reel with a reel flange at each end of the belt reel. The belt reel has a diameter greater than the diameter of the opening in the side wall. The belt carrier is inserted between the side walls bent apart in V-shape. The belt carrier is held at the height of the openings and the end walls moved together to a parallel position.