PURPOSE: To assuredly seal a container, and facilitate the unsealing by fixing a plastic sealing plate on the internal side of a short cylindrical part of a flange forming body by an easily unsealable adhesive layer.

CONSTITUTION: For a plastic container, a flange part 12 which extends outward is formed at an opening 11 of a container body 1, and a flange forming body 21 consisting of a short cylindrical part 211 to fit the opening 11, and a lid flange 212 being formed on the upper end external side of the short cylindrical part 211 is fitted in the opening 11. Thus, the flange part 12 and lid flange 212 are firmly adhered, and at the same time, a plastic 7 sealing plate 22 is fixed on the internal side of the short cylindrical part 211 of the flange forming body 21 by an easily unsealable adhesive layer 3. Also, a lid body 2 to be fitted is formed by fixing the plastic sealing plate 22, and the lid body 2 to be fitted is fitted in the container body 1. Then, a laminated flange 23 is made by heat- bonding the flange part 12 of the container body 1 and the lid flange 212, and the laminated flange 23 is bent downward to go along the external surface of the container body. Therefore, a sealing can be done firmly enough without taking an easily openable property under consideration, and the unsealing is facilitated by peeling the sealing plate.