To provide a high-frequency heat-sealing apparatus capable of achieving a satisfactory seal in which a sealed zone is narrower in its width than at its central portion and in which contaminants such as liquid beverages are not present between thermoplastic material layers over the longitudinal direction of the sealed zone. An apparatus for transversely heat-sealing a tubular packing material made of a laminate including a synthetic resin layer and a conductive material layer, together with a fluid in which a ridge shaped to contain an arcuate partial curve in its transverse contour is so formed on the action face of a high-frequency coil flush with the flat action face of one of the pressing members that it can press the central portion of a sealed zone having two rounded and narrowed right and left sides and a flash portion for a molten thermoplastic resin is formed adjacent to the outer side on the cutting side of the high-frequency coil. IMAGE
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