[Problems] To provide a cycloolefin addition polymer that is capable of satisfying high heat resistance and high refractive index simultaneously, a composite material of the cycloolefin addition polymer with an inorganic material, and a molded article thereof.[Means for Solution] A cycloolefin addition polymer consisting essentially of a cycloolefin monomer unit and containing as an essential component a norbornene monomer unit having an aromatic ring. The cycloolefin addition polymer is preferably a cycloolefin addition polymer that consists essentially of a norbornene monomer unit having an aromatic ring. The cycloolefin addition polymers are excellent in heat resistance and have a high refractive index. The composite material is comprised of the cycloolefin addition polymer and an inorganic material. The molded article is obtained by molding the cycloolefin addition polymer or the composite material.