PURPOSE: To heat-seal a plastic bag, used for holding a textile product, in a constant width securely and hermetically.

CONSTITUTION: Two sheets of film around an opening 1a of a plastic bag 1 for holding futon, etc., are put together, flattened, and placed on a sealing stand 11 with a trapezoidal section. A frame stand 12 is placed on the film. The sealing stand 11 and film are inserted into a long slit 13 in the frame stand 12. A slender heater-rest 11c of the sealing stand 11 protrudes upward through through an opening 13b of the slit 13, and the film is lifted over the surface 12b of the frame stand 12. When an electric iron is applied to the heater- rest surface 11c and moved along the surface 11c, the film is securely fixed with the frame stand 12 and pressed between the iron and heater-rest surface. Thus, a film can be uniformly heat-sealed in a constant width according to the surface of a heater-rest surface.