A high strength steel plate consisting of, as a chemical composition, by mass%: C: 0.050% to 0.100%, Si: 0% to 0.50%, Mn: 1.20% to 1.70%, P: 0.020% or less, S: 0.0050% or less, N: 0% to 0.0080%, B: 0.0003% to 0.0030%, Ti: 0.003% to 0.030%, Nb: 0.003% to 0.050%, Cr: 0% to 2.00%, Mo: 0% to 0.90%, Al: 0% to 0.100%, Cu: 0% to 0.50%, Ni: 0% to 0.50%, V: 0% to 0.100%, W: 0% to 0.50%, Ca: 0% to 0.0030%, Mg: 0% to 0.0030%, REM: 0% to 0.0030%, and a remainder consisting of Fe and impurities, wherein one or both of Cr and Mo is contained in an amount of 0.20% or greater in total, and the Cr content is 0.80% or less in a case where the Mo content is greater than 0.50%, DI which is obtained by the Formula 1 is 2.0 to 7.8, Pcm which is obtained by the Formula 2 is 0.189% or greater, a microstructure includes one or both of martensite and bainite such that a total area fraction thereof is 99% or greater, an aspect ratio of prior austenite grains is 2.0 or greater, a number fraction of cementite having a length of 1.0 μm or greater in a long axis direction with respect to cementite having a length of 0.1 μm or greater in the long axis direction is 5% or less, a plate thickness is 4.5 mm to 20 mm, and a yield strength is 885 MPa or greater, a tensile strength is 950 MPa or greater, a total elongation is 12% or greater, and a Charpy absorbed energy at -20°C is 59 J/cm 2 or greater, DI = C 0.5 × 0.34 × 1 + 0.64 × Si × 1 + 4.1 × Mn × 1 + 0.27 × Cu × 1 + 0.52 × Ni × 1 + 2.33 × Cr × 1 + 3.14 × Mo × 1.2 Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 × B in the Formulae 1 and 2, each of, [Si], [Mn], [Cu], [Ni], [Cr], [Mo],, and represents a content of each element by mass%, and 0 is substituted in a case where the element is not contained, wherein the tensile strength, the yield strength and the total elongation are measured according to JIS Z 2241, and the Charpy absorbed energy is measured according to JIS Z 2242. C: 0.050% to 0.100%, Si: 0% to 0.50%, Mn: 1.20% to 1.70%, P: 0.020% or less, S: 0.0050% or less, N: 0% to 0.0080%, B: 0.0003% to 0.0030%, Ti: 0.003% to 0.030%, Nb: 0.003% to 0.050%, Cr: 0% to 2.00%, Mo: 0% to 0.90%, Al: 0% to 0.100%, Cu: 0% to 0.50%, Ni: 0% to 0.50%, V: 0% to 0.100%, W: 0% to 0.50%, Ca: 0% to 0.0030%, Mg: 0% to 0.0030%, REM: 0% to 0.0030%, and a remainder consisting of Fe and impurities, wherein one or both of Cr and Mo is contained in an amount of 0.20% or greater in total, and the Cr content is 0.80% or less in a case where the Mo content is greater than 0.50%, DI which is obtained by the Formula 1 is 2.0 to 7.8, Pcm which is obtained by the Formula 2 is 0.189% or greater, a microstructure includes one or both of martensite and bainite such that a total area fraction thereof is 99% or greater, an aspect ratio of prior austenite grains is 2.0 or greater, a number fraction of cementite having a length of 1.0 μm or greater in a long axis direction with respect to cementite having a length of 0.1 μm or greater in the long axis direction is 5% or less, a plate thickness is 4.5 mm to 20 mm, and a yield strength is 885 MPa or greater, a tensile strength is 950 MPa or greater, a total elongation is 12% or greater, and a Charpy absorbed energy at -20°C is 59 J/cm 2 or greater, DI = C 0.5 × 0.34 × 1 + 0.64 × Si × 1 + 4.1 × Mn × 1 + 0.27 × Cu × 1 + 0.52 × Ni × 1 + 2.33 × Cr × 1 + 3.14 × Mo × 1.2 Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 × B in the Formulae 1 and 2, each of, [Si], [Mn], [Cu], [Ni], [Cr], [Mo],, and represents a content of each element by mass%, and 0 is substituted in a case where the element is not contained, wherein the tensile strength, the yield strength and the total elongation are measured according to JIS Z 2241, and the Charpy absorbed energy is measured according to JIS Z 2242.