PURPOSE: To achieve a stable shape corresponding to the minimum size of the press chamber by consisting a press element of a stiff rubber or plastic web extended to the width of the press chamber and by maintaining the loop upright corresponding to the minimum size of the press chamber by an inherent rigidity of the web.

CONSTITUTION: A press chamber PM is formed by a self-supported loop (SM) made of a web press element 9 and the press material is held and guided on a plurality of rollers W, WS, W1 and W2. The press element 9 comprises of a rubber or plastic web with the thickness (d) of about 5-10 mm being extended to the entire width of the press chamber. The direction of the rubber or plastic web is so flexible as to be changeable around the rollers W1 and W2. It is further provided with an inherent rigidity sufficient for preventing the self-supported loop (SM) which defines the minimum size of the press chamber PM from being broken and maintaining the press chamber 9 in the form of a loop.