A steel plate having a chemical composition consisting of, in terms of mass%: C: 0.07 to 0.10%; Si: 0.01 to 0.10%; Mn: 0.5 to 1.5%; Ni: 0.5 to 3.5%; Cr: 0.1 to 1.5%; Mo: 0.1 to 1.0%; V: 0.005 to 0.070%; Al: 0.01 to 0.10%; B: 0.0005 to 0.0020%; N: 0.002 to 0.010%; P: 0.006% or less; S: 0.003% or less; Cu: 0 to 1%; Nb: 0 to 0.05%; Ti: 0 to 0.020%; Ca: 0 to 0.0030%; Mg: 0 to 0.0030%; REM: 0 to 0.0030%; Sb: 0 to 0.02%; As: 0 to 0.02%; Sn: 0 to 0.02%; Pb: 0 to 0.1%; Zr: 0 to 0.1%; Zn: 0 to 0.1%; W: 0 to 0.1%; and Co: 0 to 0.2%; and the remainder being Fe and impurity, wherein an α value defined by expression 1 is 0.13 to 1.0 mass%, and a β value defined by expression 2 is 8.45 to 15.2, a yield strength is 670 to 870 N/mm 2 and a tensile strength is 780 to 940 N/mm 2, a grain is defined as an area surrounded by a boundary in which a misorientation is 30° or more and which is identified by performing an orientation analysis using an electron beam backscatter diffraction pattern analysis method, a grain size is defined as an equivalent circle diameter of the grain, an average grain size is defined as a grain size at which a cumulative frequency is 90% when a frequency distribution of the grain size is cumulated from a small grain size side, and the average grain size at mid-thickness of the steel plate is 35 μm or less, a plate thickness is 25 to 200 mm, α = ′ C ′ + 6 + ′ Si ′ + 100 × ′ P ′ β = 0.65 × ′ C ′ 1 / 2 × 1 + 0.64 × ′ Si ′ × 1 + 4.10 × ′ Mn ′ × 1 + 0.27 × ′ Cu ′ × 1 + 0.52 × ′ Ni ′ × 1 + 2.33 × ′ Cr ′ × 1 + 3.14 × ′ Mo ′ and 'C', 'Si', 'P', 'Mn', 'Cu', 'Ni', 'Cr', and 'Mo' indicate amounts of C, Si, P, Mn, Cu, Ni, Cr, and Mo in terms of mass%, respectively. C: 0.07 to 0.10%; Si: 0.01 to 0.10%; Mn: 0.5 to 1.5%; Ni: 0.5 to 3.5%; Cr: 0.1 to 1.5%; Mo: 0.1 to 1.0%; V: 0.005 to 0.070%; Al: 0.01 to 0.10%; B: 0.0005 to 0.0020%; N: 0.002 to 0.010%; P: 0.006% or less; S: 0.003% or less; Cu: 0 to 1%; Nb: 0 to 0.05%; Ti: 0 to 0.020%; Ca: 0 to 0.0030%; Mg: 0 to 0.0030%; REM: 0 to 0.0030%; Sb: 0 to 0.02%; As: 0 to 0.02%; Sn: 0 to 0.02%; Pb: 0 to 0.1%; Zr: 0 to 0.1%; Zn: 0 to 0.1%; W: 0 to 0.1%; and Co: 0 to 0.2%; and the remainder being Fe and impurity, wherein an α value defined by expression 1 is 0.13 to 1.0 mass%, and a β value defined by expression 2 is 8.45 to 15.2, a yield strength is 670 to 870 N/mm 2 and a tensile strength is 780 to 940 N/mm 2, a grain is defined as an area surrounded by a boundary in which a misorientation is 30° or more and which is identified by performing an orientation analysis using an electron beam backscatter diffraction pattern analysis method, a grain size is defined as an equivalent circle diameter of the grain, an average grain size is defined as a grain size at which a cumulative frequency is 90% when a frequency distribution of the grain size is cumulated from a small grain size side, and the average grain size at mid-thickness of the steel plate is 35 μm or less, a plate thickness is 25 to 200 mm, α = ′ C ′ + 6 + ′ Si ′ + 100 × ′ P ′ β = 0.65 × ′ C ′ 1 / 2 × 1 + 0.64 × ′ Si ′ × 1 + 4.10 × ′ Mn ′ × 1 + 0.27 × ′ Cu ′ × 1 + 0.52 × ′ Ni ′ × 1 + 2.33 × ′ Cr ′ × 1 + 3.14 × ′ Mo ′ and 'C', 'Si', 'P', 'Mn', 'Cu', 'Ni', 'Cr', and 'Mo' indicate amounts of C, Si, P, Mn, Cu, Ni, Cr, and Mo in terms of mass%, respectively.