A copolymer contains 10 to 69 mol % of a structural unit derived from propylene, 1 to 50 mol % of a structural unit derived from at least one .alpha.-olefin having a carbon number of from 4 to 20 and 30 to 89 mol % of a structural unit derived from at least one cyclic olefin represented by the formula (1) as defined herein, and has a weight average molecular weight of from 50,000 to 1,000,000.