The present invention has for its object to provide a curable composition which, despite its low viscosity, gives a cured product with a high gel fraction, low residual tack, low modulus, high elongation, and good flexibility.The present invention relates to a curable composition comprising the following two components: (A) a vinyl polymer having at least one crosslinking silyl group on the average per molecule: and (B) a photocurable substance, (C) an air oxidation-curable substance, (D) a high molecular plasticizer, (E) a reactive plasticizer or (F) a compound having one silanol group in its molecule and/or a compound capable of reacting with moisture to give a compound having one silanol group in the molecule.