The present invention provides a curable composition, which contains a crosslinking aid (B) containing three or more allyl groups in the molecule in an amount of 1 to 50 parts by mass, polyfunctional (meth)acrylic compound (C) in an amount of 5 to 50 parts by mass, and photopolymerization initiator (D1) and/or thermal polymerization initiator (D2) in an amount of 0.1 to 10 parts by mass, respectively, as a polymerization initiator (D) to 100 parts by mass of allyl group-terminated allyl ester oligomer (A); wherein the crosslinking aid (B) containing allyl group is a compound containing three or more allyl groups in a molecule; wherein the content of impurities derived from the crosslinking aid (B) in the curable composition is less than 0.1 mass %; wherein the content of the (meth)acrylic compound containing a hydroxyl group in a molecule (C1) in the curable composition is 0.5 to 30 mass %.