A molded foam containing no voids and a mold for forming such a molded foam are provided. A molded foam 5 has an external corner 5 a where a small rib 10 is formed and a recessed step 7 where thin plate-like ribs 11 are formed. The rib 10 has a triangular cross-sectional shape in a direction perpendicular to the longitudinal direction of the recessed step 7 . The rib 10 is tapered from the base to an end thereof in a direction in which the rib 10 protrudes. The ribs 11 are arranged at intervals in the longitudinal direction of the recessed step 7.