To provide a norbornene-based addition copolymer obtained by copolymerizing (a) a norbornene-based monomer having a carbon-carbon unsaturated bond in addition to a norbornene ring.

The norbornene-based addition copolymer including an unsaturated bond is obtained by addition copolymerizing (a) a norbornene-based monomer having a carbon-carbon unsaturated bond in addition to a norbornene ring and (b) a norbornene-based monomer having no carbon-carbon unsaturated bond in addition to a norbornene ring with the use of a polymerization catalyst composed of (A) a compound of a group 10 transition metal in the periodic table having an alkyl group or an aryl group and a neutral electron donative monodentate ligand and (B) a Lewis acid, in which the norbornene-based addition copolymer has 20-95 mol% repeating units content derived from monomers (a) and has a number average molecular weight of 16,800-1,000,000 when measured by the gel permeation chromatography in terms of polystyrene.