A method of producing a lid including a top plate and a side wall extending downward from a periphery of the top plate, using molds, the molds including a papermaking mold and a drying mold. The top plate is provided with an abutting part abutting against an edge of an opening of a container, while an undercut part to be fitted to a lower part of the edge is formed on the side wall so as to be located below the abutting part. The papermaking mold is provided with suction holes at a level corresponding to a level of the undercut part formed on an inner surface of the side wall. The side wall is suctioned using the suction holes when a molded article is at least in one of several states to form the undercut part in a convex shape on the inner surface of the side wall.