Abstract: A tube-forming apparatus in a bag-forming, filling, and sealing machine has a longitudinal seam heat-sealing device for connecting edge regions of the packing material belt that are placed against each other inside surface to inside surface. In order to achieve a sufficient sealing temperature in a short time, a heating body that is embodied in a lamella-like fashion protrudes like a tongue between the edge regions. In order to aid the heating body, similar heating bodies rest against the outside of the edge regions. The heating bodies have a U-shaped electric resistance wire with elongated legs which is embedded in a longitudinally folded casing made of a thin, temperature-proof woven cloth.