A method for manufacturing a sealing device, the sealing device being an elastomeric sealing device that is fitted in an annular fitting groove formed on one of two members (200, 300) so as to seal an annular gap between the two members (200, 300), the two members (200, 300) configured to be reciprocally movable relative to each other, said method including: conducting a process for molding an elastomeric cylindrical molded body by a molding mechanism having an inner mold of a substantially columnar shape, an outer mold of a substantially cylindrical shape, and a lower mold arranged at a lower side of these molds (521, 522), wherein the molded body is provided with a plurality of cylindrical surface portions and a plurality of annular outer peripheral convex portions arranged alternately on an outer peripheral side thereof, and further provided with a plurality of cylindrical surface portions and a plurality of annular inner peripheral convex portions arranged alternately on an inner peripheral side thereof, the cylindrical surface portions on the outer peripheral side and the cylindrical surface portions on the inner peripheral side are provided so as to be at the same positions in an axial direction, the outer peripheral convex portions and the inner peripheral convex portions are also provided so as to be at the same positions in the axial direction, and the cross sectional shapes thereof are of a symmetrical configuration with respect to their centerline in a radial direction; and conducting a process for conducting a parting operation to the molded body along the individual cylindrical surface portions on the outer peripheral side, characterized in that the projection height of the outer peripheral convex portion of the sealing device obtained by the process for conducting a parting operation is set to be higher than the projection height of the inner peripheral convex portion thereof, and the process for molding includes moving the inner mold in a lower direction together with the lower mold, in a state where the molded body is held inside the outer mold, after having been molded by the molding mechanism, and then taking out the molded body from the outer mold. conducting a process for molding an elastomeric cylindrical molded body by a molding mechanism having an inner mold of a substantially columnar shape, an outer mold of a substantially cylindrical shape, and a lower mold arranged at a lower side of these molds (521, 522), wherein the molded body is provided with a plurality of cylindrical surface portions and a plurality of annular outer peripheral convex portions arranged alternately on an outer peripheral side thereof, and further provided with a plurality of cylindrical surface portions and a plurality of annular inner peripheral convex portions arranged alternately on an inner peripheral side thereof, the cylindrical surface portions on the outer peripheral side and the cylindrical surface portions on the inner peripheral side are provided so as to be at the same positions in an axial direction, the outer peripheral convex portions and the inner peripheral convex portions are also provided so as to be at the same positions in the axial direction, and the cross sectional shapes thereof are of a symmetrical configuration with respect to their centerline in a radial direction; and conducting a process for conducting a parting operation to the molded body along the individual cylindrical surface portions on the outer peripheral side, characterized in that the projection height of the outer peripheral convex portion of the sealing device obtained by the process for conducting a parting operation is set to be higher than the projection height of the inner peripheral convex portion thereof, and the process for molding includes moving the inner mold in a lower direction together with the lower mold, in a state where the molded body is held inside the outer mold, after having been molded by the molding mechanism, and then taking out the molded body from the outer mold.