A foil web of indefinite length is advanced in a taut condition along one part of its path of travel by a series of jaws clamped along both lateral edges of the web. The jaws are attached to the links of two endless chains disposed at either side of the web. Those terminal sprockets of the two chains that are at the run-in location of the web are slightly inclined to one another, so that the distance between the two said sprockets at the run-in side of the chains is slightly larger than at the run-off side. Between the two said sprockets there is rotatably held a web guiding drum which positions the running web at the height of the jaws as they run off the sprockets at the run-in side of the web.