A curable composition having a low viscosity and providing a satisfactory rubber cured article is provided. A composition curable by radical photo curing and cationic photo curing in combination, comprising the under-mentioned components (A), (B), (C) and (D) as essential components: (A) a vinyl polymer having two or more acryloyl group or the like per molecule, the acryloyl groups or the like being present at one or more molecular ends; (B) an epoxy compound and/or an oxetane compound; (C) a radical photopolymerization initiator; and (D) a cationic photopolymerization initiator.