A steel plate, wherein the steel plate includes, as a chemical composition, by mass%, C: 0.030% to 0.070%, Si: 0.005% to 0.50%, Mn: 1.05% to 1.65%, Al: 0.010% to 0.070%, Ti: 0.005% to 0.020%, Nb: 0.005% to 0.045%, Ca: 0.0010% to 0.0050%, N: 0.0015% to 0.0070%, Ni: 0% to 0.50%, Mo: 0% to 0.50%, Cr: 0% to 0.50%, Cu: 0% to 0.50%, V: 0% to 0.100%, Mg: 0% to 0.0100%, REM: 0% to 0.0100%, P: limited to 0.015% or less, S: limited to 0.0015% or less, O: limited to 0.0040% or less, and a remainder of Fe and impurities, Ceq defined by the following Expression in the chemical composition is 0.300 to 0.400, a surface layer microstructure that is a microstructure in a range up to 1.0 mm from a surface of the steel plate in a depth direction includes a polygonal ferrite and a granular bainite, an area fraction of the polygonal ferrite in the surface layer microstructure is 0 to 70%, which is determined in accordance with a method disclosed in the description, a total area fraction of the polygonal ferrite and the granular bainite in the surface layer microstructure is 50% or more, which is determined in accordance with a method disclosed in the description, a maximum hardness in the surface layer microstructure is 270 Hv or lower, which is determined in accordance with a method disclosed in the description, an area fraction of a polygonal ferrite in an internal microstructure that is a microstructure in a range up to a thickness center from an area positioned at a distance of more than 1.0 mm from the surface of the steel plate in the depth direction is 40% or less, which is determined in accordance with a method disclosed in the description, wherein a remainder of the internal microstructure consists of one or more selected from the group consisting of a granular bainite, a bainite, and a pseudo pearlite, a maximum hardness in the internal microstructure is 248 Hv or lower, which is determined in accordance with a method disclosed in the description, and an average hardness in the internal microstructure is 150 to 220 Hv, which is determined in accordance with a method disclosed in the description, Ceq = C + Mn / 6 + Ni + Cu / 15 + Cr + Mo + V / 5 where, [Mn], [Ni], [Cu], [Cr], [Mo], and represent the amounts of C, Mn, Ni, Cu, Cr, Mo, and V by mass%. wherein the steel plate includes, as a chemical composition, by mass%, C: 0.030% to 0.070%, Si: 0.005% to 0.50%, Mn: 1.05% to 1.65%, Al: 0.010% to 0.070%, Ti: 0.005% to 0.020%, Nb: 0.005% to 0.045%, Ca: 0.0010% to 0.0050%, N: 0.0015% to 0.0070%, Ni: 0% to 0.50%, Mo: 0% to 0.50%, Cr: 0% to 0.50%, Cu: 0% to 0.50%, V: 0% to 0.100%, Mg: 0% to 0.0100%, REM: 0% to 0.0100%, P: limited to 0.015% or less, S: limited to 0.0015% or less, O: limited to 0.0040% or less, and a remainder of Fe and impurities, Ceq defined by the following Expression in the chemical composition is 0.300 to 0.400, a surface layer microstructure that is a microstructure in a range up to 1.0 mm from a surface of the steel plate in a depth direction includes a polygonal ferrite and a granular bainite, an area fraction of the polygonal ferrite in the surface layer microstructure is 0 to 70%, which is determined in accordance with a method disclosed in the description, a total area fraction of the polygonal ferrite and the granular bainite in the surface layer microstructure is 50% or more, which is determined in accordance with a method disclosed in the description, a maximum hardness in the surface layer microstructure is 270 Hv or lower, which is determined in accordance with a method disclosed in the description, an area fraction of a polygonal ferrite in an internal microstructure that is a microstructure in a range up to a thickness center from an area positioned at a distance of more than 1.0 mm from the surface of the steel plate in the depth direction is 40% or less, which is determined in accordance with a method disclosed in the description, wherein a remainder of the internal microstructure consists of one or more selected from the group consisting of a granular bainite, a bainite, and a pseudo pearlite, a maximum hardness in the internal microstructure is 248 Hv or lower, which is determined in accordance with a method disclosed in the description, and an average hardness in the internal microstructure is 150 to 220 Hv, which is determined in accordance with a method disclosed in the description, Ceq = C + Mn / 6 + Ni + Cu / 15 + Cr + Mo + V / 5 where, [Mn], [Ni], [Cu], [Cr], [Mo], and represent the amounts of C, Mn, Ni, Cu, Cr, Mo, and V by mass%.