It has been discovered that an initiation reaction is efficiently progressed to a propagation reaction by adding a compound that potentially or directly generates a carbocation to the polymerization system of a cationic ring-opening polymerizable compound, and thus the activation of polymerization is rendered. Namely, the present invention relates to a cationic polymerizable resin composition which is characterized by comprising (A) a compound having at least one functional group capable of cationic ring-opening polymerization in one molecular chain, (B) a cationic polymerization initiator, and (C) a compound to generate a carbocation by the action of active species generated from (B) the cationic polymerization initiator by electromagnetic wave or particle beam. According to the present invention, it has been discovered that the initiation reaction is efficiently progressed to the propagation reaction by adding the compound that potentially or directly generates a carbocation to the polymerization system of the cationic ring-opening polymerizable compound, and thus the activation of polymerization is rendered.