Provided are: a thermoplastic elastomer composition, excellent in both abrasion resistance and mechanical characteristics, obtained by heat-treating a mixture under molten condition thereof, the mixture including: 100 parts of at least one addition-polymerized block copolymer selected from a block copolymer and a hydrogenated product thereof; the block copolymer has a polymer block mainly including a structural unit derived from an aromatic vinyl compound and containing 1% by mass or more of a structural unit derived from a styrene having an alkyl group bonded to a benzene ring and a polymer block mainly including a structural unit derived from a conjugated diene compound, 10 to 300 parts olefin-based resin, 0.01 to 20 parts crosslinking agent; 1 to 50 parts crosslinking adjuvant containing one methacryloyl group, one acryloyl group, and one or more hydroxyl group, and 30 to 250 parts rubber softener; and a molded article including the said thermoplastic elastomer composition.