Abstract: In addition to a sewing machine, a sewing unit has a workpiece holder, which has two workpiece bearing plates displaceable relative to each other, a holding bar, a folding, bar, a thrower device, a cloth slider and a folding device. By these devices, first and second trouser parts having rim strips are faced and overlapped inside-out onto a zipper. The front inseam is sewn, then the rim strip of the second trouser part is folded over and a first zipper seam is sewn. The second trouser part is folded over right-side out and the j-seam is sewn. The rim strips of the first and second trouser parts can be folded before sewing, seam locks can be provided, and a lower covering strip can be provided to the zipper as well. Thus, all three seams can be sewn with a single sewing arrangement.