[Problem] The purpose of the invention is to provide: a thermoplastic elastomer composition capable of providing molded articles that are lightweight, have better oil resistance than those provided by conventional cross-linked thermoplastic elastomers, and have hardness and mechanical properties such as tensile strength and tensile elongation that are equal to or superior to those provided by conventional cross-linked thermoplastic elastomers; and an ethylene/α-olefin/unconjugated polyene copolymer having little compression set at low temperature as well as flexibility and an excellent balance of rubber elasticity at low temperature and tensile strength at normal temperature.[Solution] Produced are: a thermoplastic elastomer composition obtained by dynamically crosslinking a mixture containing a crystalline olefin polymer (A), an ethylene/α-olefin (having 4-20 carbon atoms)/unconjugated polyene copolymer (1B) that satisfies specific requirements, and a phenol resin-based crosslinking agent (C); and an ethylene-α-olefin/unconjugated polyene copolymer (2B) that satisfies specific requirements.