PURPOSE: To perform sealing and fusing without wrinkle by sealing and fusing the vertical edge of a cylindrical body crude material made of polyethylene sheet with the peripheral edge of a circular cover crude material.

CONSTITUTION: One edge of a body crude material 1 composed in a cylindrical shape of a polyethylene sheet is suspended outside over the upper end 3 inward from a cylindrical guide 2 to form a suspended edge 4. On the other hand, the peripheral edge 6 of a cover crude material 5 composed in a larger-diameter cylindrical shape than that of the body crude material 1 made of a polyethylene sheet is bent, and superposed on the suspended edge 4. Then, the guide 2 is rotated by a driving motor 9 while a heater 8 is brought into contact with the superposed parts to seal the edge 4 with the peripheral edge 6, and to fuse it off at the outside.