A steel plate, comprising: a chemical composition consisting of, by mass%, C: 0.020 % to 0.090 %, Si: 0.01 % to 0.35 %, Mn: 1.40 % to 2.00 %, P: 0.008 % or less, S: 0.0035 % or less, Al: 0.010 % to 0.060 %, Ni: 0.40 % to 2.00 %, Mo: 0.05 % to 0.50 %, Nb: 0.005 % to 0.040 %, Ti: 0.005 % to 0.025 %, N: 0.0020 % to 0.0050 %, Ca: 0.0005 % to 0.0050 %, and O: 0.0035 % or less, Ceq specified by formula below being in a range of 0.420 % to 0.520 %, formulas , , and below being satisfied, optionally at least one selected from the group consisting of, by mass%, Cu: less than 0.7 %, Cr: 0.1 % to 1.0 %, V: 0.005 % to 0.05 % Mg: 0.0002 % to 0.0050 % and a REM: 0.0010 % to 0.0200 %, and the balance being Fe and incidental impurities including B of less than 0.0003 %; and precipitates including Ti, Nb, and Mo and having a mean particle size of 2 nm or more and 20 nm or less, wherein [Nb]/([Ti] + [Nb] + [Mo]) ≥ 0.3, where [Ti] is the Ti content in the precipitates, [Nb] is the Nb content in the precipitates, and [Mo] is the Mo content in the precipitates: Ceq = C + Mn / 6 + Cu + Ni / 15 + Cr + Mo + V / 5 1.5 ≤ Ti / N ≤ 4.0 0 < Ca − 0.18 + 130 × Ca × O / 1.25 / S < 1.5 5.5 C 4 / 3 + 15 P + 0.90 Mn + 0.12 Ni + 7.9 Nb 1 / 2 + 0.53 Mo ≤ 3.70 where [M] is the content of element M by mass%, and a thickness of the steel plate is 15 mm or more, and wherein the steel plate has a YS of 460 MPa or more, a TS of 570 MPa or more, a Charpy absorbed energy vE -40 °C of 200 J or more, a ΔTS of 5 MPa to -15 MPa, and a ΔvTrs of 10 °C to -5 °C, where ΔTS is the change in tensile strength in the base metal before and after post weld heat treatment, and ΔvTrs is the change in toughness in the base metal before and after post weld heat treatment. a chemical composition consisting of, by mass%, C: 0.020 % to 0.090 %, Si: 0.01 % to 0.35 %, Mn: 1.40 % to 2.00 %, P: 0.008 % or less, S: 0.0035 % or less, Al: 0.010 % to 0.060 %, Ni: 0.40 % to 2.00 %, Mo: 0.05 % to 0.50 %, Nb: 0.005 % to 0.040 %, Ti: 0.005 % to 0.025 %, N: 0.0020 % to 0.0050 %, Ca: 0.0005 % to 0.0050 %, and O: 0.0035 % or less, Ceq specified by formula below being in a range of 0.420 % to 0.520 %, formulas , , and below being satisfied, optionally at least one selected from the group consisting of, by mass%, Cu: less than 0.7 %, Cr: 0.1 % to 1.0 %, V: 0.005 % to 0.05 % Mg: 0.0002 % to 0.0050 % and a REM: 0.0010 % to 0.0200 %, and the balance being Fe and incidental impurities including B of less than 0.0003 %; and precipitates including Ti, Nb, and Mo and having a mean particle size of 2 nm or more and 20 nm or less, wherein [Nb]/([Ti] + [Nb] + [Mo]) ≥ 0.3, where [Ti] is the Ti content in the precipitates, [Nb] is the Nb content in the precipitates, and [Mo] is the Mo content in the precipitates: Ceq = C + Mn / 6 + Cu + Ni / 15 + Cr + Mo + V / 5 1.5 ≤ Ti / N ≤ 4.0 0 < Ca − 0.18 + 130 × Ca × O / 1.25 / S < 1.5 5.5 C 4 / 3 + 15 P + 0.90 Mn + 0.12 Ni + 7.9 Nb 1 / 2 + 0.53 Mo ≤ 3.70 where [M] is the content of element M by mass%, and a thickness of the steel plate is 15 mm or more, and wherein the steel plate has a YS of 460 MPa or more, a TS of 570 MPa or more, a Charpy absorbed energy vE -40 °C of 200 J or more, a ΔTS of 5 MPa to -15 MPa, and a ΔvTrs of 10 °C to -5 °C, where ΔTS is the change in tensile strength in the base metal before and after post weld heat treatment, and ΔvTrs is the change in toughness in the base metal before and after post weld heat treatment. <EOS>