To provide a mold capable of simply conducting the molding operation of an inlet and shortening a molding cycle.

An enlarging unit 1 for molding an enlarged inlet is provided in an inner mold A to be press injected to the end of a heated and softened synthetic resin tube. On the other hand, an outer mold B has a flange 41 brought into close contact with the end of the inlet at the one end of a cylinder 4 having an inner diameter larger than the outer diameter of the enlarged inlet, a flange 5 made of soft and hard rubbers brought into close contact with the outer periphery of the tube near the rear end of the inlet at the other end, and a backup member 6 movably arranged at the outside of the flange 5. Thus, the molding operation of the inlet can be simply executed, the molding cycle can be shortened, and no leakage of pressurized fluid occurs from the outer mold.