To provide a polymer solution suitable for forming by a cast film-forming method, spin coat method, solution spinning method or the like, although it is a polymer solution including a copolymer obtained by polymerizing norbornene and ethylene.

The polymer solution to be used is obtained by dissolving a terpolymer produced by polymerizing ethylene, norbornene and a monomer other than ethylene and norbornene in a solvent. Here the content of a repeating unit derived from ethylene is 60 mol% or less, the content of a repeating unit derived from the above monomer to the total amount of the content of a repeating unit derived from norbornene and the content of a repeating unit derived from the above monomer is 0.01-20 mol%, the glass transition temperature of the terpolymer is 100°C or higher, and the number-average molecular weight of the terpolymer in terms of polystyrene calculated from the gel permeation chromatography is 10,000-200,000.