To widen the range of a heat-sealing condition and obtain a stable peeling strength, by laminating heat-sealing film composed of a heat-seal layer formed of a mixture of polyethylene and polystyrene and a base material film.

Base material film 1 containing paper is laminated together with heat-sealing film 5 (HS) to form a heat-sealing cover material 10. The HS film 5 is constituted of a heat-seal layer 7 made of a mixture of polyethylene and polystyrene and a carrier layer 6 (10-65 mm thick). The heat-seal layer 7 directly sealed with the container is made thin and stabilized as film by adding the carrier layer 6 thereto. The thickness of the heat-seal layer 7 is preferably 3-20 μm. Not only peeling of paper is prevented as the peeling strength is partly increased in the range of the thickness, but also the appearance of the peeling part is not spoiled.