SYNTHETIC RESIN CAP, CLOSING DEVICE, AND CLOSING DEVICE WITH BEVERAGE

摘要

PROBLEM TO BE SOLVED: To provide a synthetic resin cap capable of preventing container internal pressure from excessively rising.SOLUTION: A synthetic resin cap includes a top plate part and a cylindrical part hanging from its circumference. An inner seal projection 12 fitted into the mouth part and an outer projection 14 that contacts the external surface of the mouth part are formed in the inner surface of the top plate part. The inner seal projection 12 can contact the inner surface of the mouth part in a pressurized state. One or a plurality of abutting convex parts 15 that contact the external surface of the mouth part in a pressurized state are formed in the inner surface 14a of the outer projection 14. At least a portion of the part where abutting convex parts 15 are not formed of the inner surface 14a of the outer projection 14 is away from the external surface of the mouth part.