A cyclic-olefin-based copolymer according to a first embodiment of the present invention includes: a constituent unit (A) derived from an α-olefin having 2-20 carbon atoms; a constituent unit (B) derived from a cyclic olefin that does not have an aromatic ring; and a constituent unit (C) derived from a cyclic olefin that has an aromatic ring. A medical container according to a second embodiment of the present invention contains the cyclic-olefin-based copolymer that includes: the constituent unit (A) derived from an α-olefin having 2-20 carbon atoms; the constituent unit (B) derived from a cyclic olefin that does not have an aromatic ring; and the constituent unit (C) derived from a cyclic olefin that has an aromatic ring.