Provided is a curable composition including (A) an addition reaction product of (a) a compound with 2 silicon atom-bonded hydrogen atoms within each molecule, having a general formula (1): ##STR00001## wherein, A is a bivalent group represented by a formula (2): ##STR00002## (wherein, R' represents an unsubstituted or substituted monovalent hydrocarbon group of 1 to 12 carbon atoms, or an alkoxy group of 1 to 6 carbon atoms, and n represents an integer from 0 to 100), or a group having a structural formula (3): ##STR00003## and each R represents an unsubstituted or substituted monovalent hydrocarbon group of 1 to 12 carbon atoms, or an alkoxy group of 1 to 6 carbon atoms, and (b) a polycyclic hydrocarbon with 2 addition reactive carbon-carbon double bonds within each molecule, said addition reaction product containing at least two addition reactive carbon-carbon double bonds in each molecule, (B) a compound with at least 3 silicon atom-bonded hydrogen atoms within each molecule, and (C) a hydrosilylation reaction catalyst. This composition is useful as a material for optical devices or parts, insulation material for electronic devices or parts, or coating material.