To provide a pipe socket structure wherein capable of easily inserting an elastic seal ring into an inner surface of the socket thereof, being superior in workability, and having a coming-off preventive function.

In a pipe socket structure, a ring 10 is held on a socket inner surface of the pipe. The ring 10 is integrally composed of an elastic seal portion 11 and a groove molding synthetic resin portion 12 for molding an end groove of the pipe. The groove molding synthetic resin portion 12 has a projection 9 on the inside in the radial direction so as to be fitted in a groove of an outer surface of a pipe insertion port.