Disclosed is a curable composition having excellent curability, which is capable of forming a cured product that is excellent in heat resistance, weather resistance, oil resistance and the like, while having rubber elasticity and high mechanical strength. Specifically disclosed is a curable composition for both photoradical and thermal radical curing essentially containing the following components (A), (B), and (C). (A) a vinyl-based polymer having two or more groups represented by the general formula (1): —OC(O)C(Ra)═CH2  (1) wherein Ra represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, per molecule, and having one or more groups represented by the above general formula (1) at a molecular terminal; (B) a photoradical initiator; and (C) a thermal radical initiator, as essential components.