A steel sheet comprising a chemical composition that contains, in mass %: C: 0.18% to 0.35%, Si: 0.01% to 1.00%, Mn: 0.10% to 2.40%, P: 0.050% or less, S: 0.0050% or less, Al: 0.001% to 1.00%, Ti: 0.001% to 0.050%, B: 0.0005% to 0.0050%, N: 0.0100% or less, O: 0.0050% or less, Cr: 0% to 1.00%, Mo: 0% to 0.50%, Cu: 0% to 0.50%, Ni: 0% to 0.50%, Co: 0% to 0.50%, W: 0% to 0.50%, Sn: 0% to 0.50%, Sb: 0% to 0.50%, Nb: 0% to 0.050%, V: 0% to 0.50%, Ca: 0% to 0.0100%, Mg: 0% to 0.0100%, Ce: 0% to 0.0100%, Zr: 0% to 0.0100%, La: 0% to 0.0100%, Hf: 0% to 0.0100%, Bi: 0% to 0.0100%, REM: 0% to 0.0100%, and a balance consisting of Fe and impurities, and that satisfies the Formula: 0.001 ≤ Ti-(47.88/14.01) × N ≤ 0.040, wherein each element symbol represents mass % of the corresponding element, and a steel structure in a cross section in a rolling direction of a steel sheet and in a range of 1/8 thickness to 3/8 thickness centered on 1/4 thickness from a surface of the steel sheet, that contains, in area ratio%, ferrite: 0 to 5%, martensite: 90.0 to 99.5%, a ratio of tempered martensite to total martensite: 80.0 to 100.0%, and retained austenite: 0.5 to 6.0%, and in a measurement region defined by a range of 1/8 thickness to 7/8 thickness from the surface of the steel sheet × 25 mm in the cross section in the rolling direction of the steel sheet, a number density of inclusions satisfying a maximum diameter ≥ 3 μm is 40 inclusions/mm 2 or less, when the measurement region is divided into 100 sections obtained by dividing the measurement region into 2 sections in a thickness direction and 50 sections in a width direction, and the number density of the inclusions satisfying the maximum diameter ≥ 3 μm in each section is calculated, the number density in a section where the number density of inclusions is in a top 10% is 80 inclusions/mm 2 or less, the following Formula is satisfied, the total elongation El of the steel sheet is 6% or more, and a tensile strength is 1470 MPa or more: Vγ ′ / Vγ ≥ 0.1 wherein Vγ: area ratio of initial retained austenite, Vγ': area ratio of retained austenite after deep cooling at -196° C, the microstructure constituents and the inclusions number density being measured according to the description. C: 0.18% to 0.35%, Si: 0.01% to 1.00%, Mn: 0.10% to 2.40%, P: 0.050% or less, S: 0.0050% or less, Al: 0.001% to 1.00%, Ti: 0.001% to 0.050%, B: 0.0005% to 0.0050%, N: 0.0100% or less, O: 0.0050% or less, Cr: 0% to 1.00%, Mo: 0% to 0.50%, Cu: 0% to 0.50%, Ni: 0% to 0.50%, Co: 0% to 0.50%, W: 0% to 0.50%, Sn: 0% to 0.50%, Sb: 0% to 0.50%, Nb: 0% to 0.050%, V: 0% to 0.50%, Ca: 0% to 0.0100%, Mg: 0% to 0.0100%, Ce: 0% to 0.0100%, Zr: 0% to 0.0100%, La: 0% to 0.0100%, Hf: 0% to 0.0100%, Bi: 0% to 0.0100%, REM: 0% to 0.0100%, and a balance consisting of Fe and impurities, and that satisfies the Formula: 0.001 ≤ Ti-(47.88/14.01) × N ≤ 0.040, wherein each element symbol represents mass % of the corresponding element, and a steel structure in a cross section in a rolling direction of a steel sheet and in a range of 1/8 thickness to 3/8 thickness centered on 1/4 thickness from a surface of the steel sheet, that contains, in area ratio%, ferrite: 0 to 5%, martensite: 90.0 to 99.5%, a ratio of tempered martensite to total martensite: 80.0 to 100.0%, and retained austenite: 0.5 to 6.0%, and in a measurement region defined by a range of 1/8 thickness to 7/8 thickness from the surface of the steel sheet × 25 mm in the cross section in the rolling direction of the steel sheet, a number density of inclusions satisfying a maximum diameter ≥ 3 μm is 40 inclusions/mm 2 or less, when the measurement region is divided into 100 sections obtained by dividing the measurement region into 2 sections in a thickness direction and 50 sections in a width direction, and the number density of the inclusions satisfying the maximum diameter ≥ 3 μm in each section is calculated, the number density in a section where the number density of inclusions is in a top 10% is 80 inclusions/mm 2 or less, the following Formula is satisfied, the total elongation El of the steel sheet is 6% or more, and a tensile strength is 1470 MPa or more: Vγ ′ / Vγ ≥ 0.1 wherein Vγ: area ratio of initial retained austenite, Vγ': area ratio of retained austenite after deep cooling at -196° C, the microstructure constituents and the inclusions number density being measured according to the description.