Abstract: The present invention refers to an apparatus and a method for forming a packaging unit consisting of an endless hose, or for sealing a prefabricated packaging unit, comprising an ultrasonic welding device including an anvil and a sonotrode, which are movable towards each other, and a means for positioning the hose material to be welded between the anvil and the sonotrode. In accordance with the present invention it is suggested that the anvil comprises two anvil parts which are movable relative to one another in the direction of the sonotrode, one of said anvil parts being implemented as a sealing anvil and the other part being implemented as a separating anvil. Hence, the apparatus according to the present invention permits the production of packaging units which end directly at the weld, i.e. in the case of which no length section of the foil material projects outwardly beyond the weld.