To correctly finish the angle part of the inner face groove of a pipe into right angles without working after forming the pipe by arranging an annular channel forming the groove on the inner circumference of a resin pipe on the inner circumference of the resin pipe.

An annular channel 6 formed out of different member from the main body of a resin pipe 1 is arranged on the inner circumference of the socket 11 of the resin pipe 1, and a groove 12 is formed out of the channel 6. In this case, projecting parts 63, 64 extending in the axial direction of the pipe are formed outside the angle parts 62, 63 of the channel 6, the outer circumferences of the projecting parts 63, 64 are formed into a taper shape becoming small diameter toward the extreme end side, and the inner circumferential face 6A is formed so as to be flush with the inner circumferential face 11A of the socket 11. When the resin pipe 1 is manufactured, on the outer circumference of a core mold wound with parting material, the separately formed channel 6 is provided, in addition pipe material is wound on the outer circumference of the core mold, and after hardening it, the core mold is drawn out. Hereby, the channel 6 is stuck to the inner circumference and the integrated resin pipe 1 is formed.