Abstract: A heat sealing device for a tubular packaging material which is made of a heat-sealable paper-base laminate having an aluminum foil layer and which is to be cut transversely thereof into lengths comprises a U-shaped high-frequency coil provided in a pressing surface of one of a pair of press members and having two straight portions extending in parallel to each other for heating the packaging material at opposite sides of each cutting portion therealong. Two strip-like magnetic members are arranged on the outer side of the respective straight portions and extend approximately over the entire length of the straight portions. Each of the two straight portions has a ridge extending longitudinally of the straight portion at each of two portions of the entire length thereof for individually applying an increased pressure to opposite side edge portions of the material. The ridge has a circular-arc contour in cross section.