An alkenyl ether-vinyl ester copolymer contains a repeating unit derived from a hydroxyl group-containing alkenyl ether represented by the following formula (1), and a repeating unit derived from a vinyl ester represented by the following formula (2): where R1, R2, and R3 each independently represents a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms; R4 represents a linear or branched alkylene group having from 2 to 4 carbon atoms; R5 represents an acyl group having from 1 to 20 carbon atoms; and p represents an integer of from 1 to 3. The alkenyl ether-vinyl ester copolymer exhibits temperature responsiveness showing a change in hydrophilicity and hydrophobicity at a prescribed temperature as a critical point and has a lower critical solution temperature to water of from 1° C. to 99° C.