PURPOSE: To prevent a mouth of a container from being deformed by a hot filling and contents in the container from leaking by employing such means as to provide a top cover part covering a mouth of cap to be mounted on the mouth of a container main body by capping and an inner and an outer ring parts suspended from the top cover part.
CONSTITUTION: A cap B is mounted on a mouth A of a container main body by capping. In this case, the cap B comprises a top cover part 101 covering an opening of the mouth A, an inner ring part 102 and an outer ring part 103, both being connected to the top cover part 101 in a suspended state. Also, a protrusion 104 which is brought into contact with an open top face of the mouth A to enhance closing properties is formed on an inner face (lower face) of the top cover part 101 positioned between the inner ring part 102 and the outer ring part 103. The outer ring part 103 is molded of a heat-resistant resin. Further, a protruding line part 105 which protrudes in a radially inward direction is formed at a lower portion of the inside of the outer ring part 103. On the other hand, the outer face of the inner ring part 102 is formed of a flatly and cylindrically curved face 102b and a tapered face 102a.