A high-strength bolt having a bolt tensile strength of at least 1200 N/mm and being excellent in delayed fracture resistance characteristics and its steel product. A high-strength bolt having its head and shank formed of a steel product, wherein the steel product is so regulated in quality that the relation between a bolt tensile strength TS (N/mm ) and a tempering temperature T ( DEG C) satisfies the following expression (1), the relation between the bolt tensile strength TS and a carbon equivalent Ceq (%) calculated from its chemical components satisfies the following expression (2), and a bolt tensile strength by hardening and tempering ranges from 1200 N/mm to 1600 N/mm . TS