PURPOSE: To obtain the subject copolymer useful for a sealant, etc., and capable of providing a cured material excellent in weather resistance and elasticity by copolymerizing a fluoroolefin and a monomer having plural ether linkages and copolymerizable therewith.

CONSTITUTION: (A) A fluoroolefin (e.g., chlorotrifluoroethylene) and (B) 1-80 mol% monomer (e.g., condensate between hydroxybutyl vinyl ether and propylene oxide) copolymerizable therewith and having two or more ether linkages are copolymerized to provide an objective copolymer with 1000-50000 number-average molecular weight and containing 20-70mol% fluoroolefin-based polymerization unit and 1-80mol% other polymerization unit having a side chain with ≥2 ether linkages, and containing ≥30mol% total polymerization units of the components (A) and (B) based on the whole polymerization units.