A steel member having a composition comprising, in % by mass: C: 0.110% or more and 0.15% or less, Si: 0.50% or more and 0.80% or less, Mn: 0.40% or more and 0.65% or less, P: exceeding 0% and 0.0060% or less, S: exceeding 0% and 0.0070% or less, Al: 0.030% or more and 0.080% or less, Cu: 0.05% or more and 0.20% or less, Ni: 0.05% or more and 0.30% or less, Cr: 1.05% or more 1.50% or less, Mo: 0.45% or more and 0.65% or less, N: 0.0030% or more and 0.0070% or less, B: 0.0003% or more and 0.0010% or less, and V: 0% or more and 0.030% or less, wherein Nb content is suppressed to 0.005% or less, Ti content is suppressed to 0.001% or less, and the total content of Ca, Mg, REM, and Zr is suppressed to 0.0010% or less, the remainder consists of iron and inevitable impurities, a thickness is 100 mm or less, and a structure in a thicknesswise central portion of the steel member satisfies the following (a) and (b), and Charpy absorbed energy at -38°C is 100 J or more: (a) the structure is at least one of tempered bainite and tempered martensite, and (b) a value represented by D/d is 54 or less, where D is an average equivalent circle diameter of crystal grains surrounded by large angle grain boundaries with crystal misorientation of 15° or more between two adjacent crystal grains, and d is a maximum diameter of grain boundary carbide. C: 0.110% or more and 0.15% or less, Si: 0.50% or more and 0.80% or less, Mn: 0.40% or more and 0.65% or less, P: exceeding 0% and 0.0060% or less, S: exceeding 0% and 0.0070% or less, Al: 0.030% or more and 0.080% or less, Cu: 0.05% or more and 0.20% or less, Ni: 0.05% or more and 0.30% or less, Cr: 1.05% or more 1.50% or less, Mo: 0.45% or more and 0.65% or less, N: 0.0030% or more and 0.0070% or less, B: 0.0003% or more and 0.0010% or less, and V: 0% or more and 0.030% or less, wherein Nb content is suppressed to 0.005% or less, Ti content is suppressed to 0.001% or less, and the total content of Ca, Mg, REM, and Zr is suppressed to 0.0010% or less, the remainder consists of iron and inevitable impurities, a thickness is 100 mm or less, and a structure in a thicknesswise central portion of the steel member satisfies the following (a) and (b), and Charpy absorbed energy at -38°C is 100 J or more: (a) the structure is at least one of tempered bainite and tempered martensite, and (b) a value represented by D/d is 54 or less, where D is an average equivalent circle diameter of crystal grains surrounded by large angle grain boundaries with crystal misorientation of 15° or more between two adjacent crystal grains, and d is a maximum diameter of grain boundary carbide. wherein Nb content is suppressed to 0.005% or less, Ti content is suppressed to 0.001% or less, and the total content of Ca, Mg, REM, and Zr is suppressed to 0.0010% or less, the remainder consists of iron and inevitable impurities, a thickness is 100 mm or less, and a structure in a thicknesswise central portion of the steel member satisfies the following (a) and (b), and Charpy absorbed energy at -38°C is 100 J or more: (a) the structure is at least one of tempered bainite and tempered martensite, and (b) a value represented by D/d is 54 or less, where D is an average equivalent circle diameter of crystal grains surrounded by large angle grain boundaries with crystal misorientation of 15° or more between two adjacent crystal grains, and d is a maximum diameter of grain boundary carbide. (a) the structure is at least one of tempered bainite and tempered martensite, and (b) a value represented by D/d is 54 or less, where D is an average equivalent circle diameter of crystal grains surrounded by large angle grain boundaries with crystal misorientation of 15° or more between two adjacent crystal grains, and d is a maximum diameter of grain boundary carbide. <EOS>