PURPOSE: To release the air trapped between a core mold and a tape spirally wound around said mold, by providing the core mold with fine grooves, applying a resin layer to the surface of said tape, and curing the resin by heating.

CONSTITUTION: A resin pipe is prepared by providing fine grooves 10 to a core mold 1 having smooth outside surface, winding a tape spirally around the core mold 1, winding thermosetting pipe-molding materials 4 and 3, a mortar layer 5, etc., on the tape, and heating the whole composite. The trapped air is released through the grooves 10 to prevent the formation of voids 7