Abstract: One embodiment provides a synthetic resin cap comprising a cap body and a circular inner seal projection. The cap body having a top plate and a cylindrical section extending downward from the periphery thereof, and a threaded section that engages with a thread of the container opening is formed in the inner peripheral surface of the cylindrical section. The inner seal projection formed on the inner surface of the top plate and fits into a container opening. The circumferential direction forming angle of the threaded section is from 600° to 720°, and the threaded section is divided into a plurality of divided threaded sections at divided sections; and the divided sections are provided at nearly equal intervals in the circumferential direction.