An H-section steel comprising, as a chemical composition, by mass%: C: 0.05% to 0.16%; Si: 0.01% to 0.50%; Mn: 0.80% to 2.00%; Ni: 0.05% to 0.50%; V: 0.01% to 0.20%; Al: 0.005% to 0.100%; Ti: 0.005% to 0.030%; N: 0.0010% to 0.0200%; S: 0.002% to 0.02%; Mg: 0.0005% to 0.005; Cr: 0% to 0.50%; Cu: 0% to 0.50%; Mo: 0% to 0.20%; Nb: 0% to 0.05%; B: 0% to 0.0020%, and a remainder consisting of Fe and impurities, wherein C eq obtained by the following Equation 1 is 0.35% to 0.50%, a thickness of a flange is 100 mm to 150 mm, an area fraction of bainite in a steel structure at a strength evaluation position which is at a 1/6 position from a surface of the flange in a length direction and at a 1/4 position from the surface in a thickness direction is 80% or more, yield strength or 0.2% proof strength is 450 MPa or more, and tensile strength is 550 MPa or more and 680 MPa or less at the strength evaluation position, an average austenite grain size in a steel structure at a toughness evaluation position which is at a 1/2 position from the surface of the flange in the length direction and at a 3/4 position from the surface in the thickness direction is 150 μm or less, and (Mg, Mn)S sulfide having a particle size of 0.005 μm to 0.5 μm is included at a density of 1.0×10 5 pieces/mm 2 to 1.0×10 7 pieces/mm 2, the (Mg, Mn)S sulfide includes, by mass%, 20 % to 80 % of Mn, 20 % to 80 % of Mg, and a remainder, and a ratio of S with respect to a total mass of S and O in the remainder is, by mass%, 50 % to 100 %; C eq = C + Mn / 6 + Cr + Mo + V / 5 + Ni + Cu / 15 here, C, Mn, Cr, Mo, V, Ni, and Cu represent the amount of each element contained by mass% and the amount of an element not contained is 0. C: 0.05% to 0.16%; Si: 0.01% to 0.50%; Mn: 0.80% to 2.00%; Ni: 0.05% to 0.50%; V: 0.01% to 0.20%; Al: 0.005% to 0.100%; Ti: 0.005% to 0.030%; N: 0.0010% to 0.0200%; S: 0.002% to 0.02%; Mg: 0.0005% to 0.005; Cr: 0% to 0.50%; Cu: 0% to 0.50%; Mo: 0% to 0.20%; Nb: 0% to 0.05%; B: 0% to 0.0020%, and a remainder consisting of Fe and impurities, wherein C eq obtained by the following Equation 1 is 0.35% to 0.50%, a thickness of a flange is 100 mm to 150 mm, an area fraction of bainite in a steel structure at a strength evaluation position which is at a 1/6 position from a surface of the flange in a length direction and at a 1/4 position from the surface in a thickness direction is 80% or more, yield strength or 0.2% proof strength is 450 MPa or more, and tensile strength is 550 MPa or more and 680 MPa or less at the strength evaluation position, an average austenite grain size in a steel structure at a toughness evaluation position which is at a 1/2 position from the surface of the flange in the length direction and at a 3/4 position from the surface in the thickness direction is 150 μm or less, and (Mg, Mn)S sulfide having a particle size of 0.005 μm to 0.5 μm is included at a density of 1.0×10 5 pieces/mm 2 to 1.0×10 7 pieces/mm 2, the (Mg, Mn)S sulfide includes, by mass%, 20 % to 80 % of Mn, 20 % to 80 % of Mg, and a remainder, and a ratio of S with respect to a total mass of S and O in the remainder is, by mass%, 50 % to 100 %; C eq = C + Mn / 6 + Cr + Mo + V / 5 + Ni + Cu / 15 here, C, Mn, Cr, Mo, V, Ni, and Cu represent the amount of each element contained by mass% and the amount of an element not contained is 0.