A curable composition, comprising: an olefin-aromatic vinyl compound-aromatic polyene copolymer satisfying the following conditions to; and an additive resin, and optionally a monomer, wherein the additive resin is one or more selected from the group consisting of a hydrocarbon-based elastomer, a polyphenylene ether, an olefin-aromatic vinyl compound-aromatic polyene copolymerized oligomer, and an aromatic polyene-based resin, wherein the hydrocarbon-based elastomer is one or more selected from the group consisting of ethylene-based elastomer, propylene-based elastomer, 1,2-polybutadiene, and hydrogenated products, wherein the 1,2-polybutadiene is liquid at 25°C, wherein the monomer is in an amount of 0 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the copolymer, wherein the monomer is one or more selected from the group consisting of an aromatic vinyl compound monomer, an aromatic polyene monomer and a polar monomer: a number average molecular weight of the copolymer is 5000 or more and 100000 or less, as measured by a gel permeation chromatography using standard polystyrene; the aromatic vinyl compound monomer is an aromatic vinyl compound having 8 or more and 20 or less carbon atoms, and a content of the aromatic vinyl compound monomer unit is 0 mass% or more and 70 mass% or less; the aromatic polyene is one or more selected from polyenes having 5 or more and 20 or less carbon atoms and having a plurality of vinyl groups and/or vinylene groups in the molecule, and a content of the vinyl groups and/or the vinylene groups derived from a unit of the aromatic polyene is 1.5 pieces or more and less than 20 pieces per number average molecular weight; and the olefin is one or more selected from olefins having 2 or more and 20 or less carbon atoms, and a total of units of the olefin monomer, the aromatic vinyl compound, and the aromatic polyene monomer is 100 mass%. an olefin-aromatic vinyl compound-aromatic polyene copolymer satisfying the following conditions to; and an additive resin, and optionally a monomer, wherein the additive resin is one or more selected from the group consisting of a hydrocarbon-based elastomer, a polyphenylene ether, an olefin-aromatic vinyl compound-aromatic polyene copolymerized oligomer, and an aromatic polyene-based resin, wherein the hydrocarbon-based elastomer is one or more selected from the group consisting of ethylene-based elastomer, propylene-based elastomer, 1,2-polybutadiene, and hydrogenated products, wherein the 1,2-polybutadiene is liquid at 25°C, wherein the monomer is in an amount of 0 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the copolymer, wherein the monomer is one or more selected from the group consisting of an aromatic vinyl compound monomer, an aromatic polyene monomer and a polar monomer: a number average molecular weight of the copolymer is 5000 or more and 100000 or less, as measured by a gel permeation chromatography using standard polystyrene; the aromatic vinyl compound monomer is an aromatic vinyl compound having 8 or more and 20 or less carbon atoms, and a content of the aromatic vinyl compound monomer unit is 0 mass% or more and 70 mass% or less; the aromatic polyene is one or more selected from polyenes having 5 or more and 20 or less carbon atoms and having a plurality of vinyl groups and/or vinylene groups in the molecule, and a content of the vinyl groups and/or the vinylene groups derived from a unit of the aromatic polyene is 1.5 pieces or more and less than 20 pieces per number average molecular weight; and the olefin is one or more selected from olefins having 2 or more and 20 or less carbon atoms, and a total of units of the olefin monomer, the aromatic vinyl compound, and the aromatic polyene monomer is 100 mass%. a number average molecular weight of the copolymer is 5000 or more and 100000 or less, as measured by a gel permeation chromatography using standard polystyrene; the aromatic vinyl compound monomer is an aromatic vinyl compound having 8 or more and 20 or less carbon atoms, and a content of the aromatic vinyl compound monomer unit is 0 mass% or more and 70 mass% or less; the aromatic polyene is one or more selected from polyenes having 5 or more and 20 or less carbon atoms and having a plurality of vinyl groups and/or vinylene groups in the molecule, and a content of the vinyl groups and/or the vinylene groups derived from a unit of the aromatic polyene is 1.5 pieces or more and less than 20 pieces per number average molecular weight; and the olefin is one or more selected from olefins having 2 or more and 20 or less carbon atoms, and a total of units of the olefin monomer, the aromatic vinyl compound, and the aromatic polyene monomer is 100 mass%.