An H-section steel has a predetermined chemical composition in which a thickness of a flange is 100 mm to 150 mm, at a strength evaluation position an area fraction of bainite in a steel structure is 80% or more, yield strength or 0.2% proof strength is 450 MPa or more, tensile strength is 550 MPa or more and 680 MPa or less, at a toughness evaluation position an average austenite grain size in the steel structure is 150 μm or less, and (Mg, Mn)S having a particle size of 0.005 μm to 0.5 μm is included at a density of 1.0×105 pieces/mm2 to 1.0×107 pieces/mm2.