A steel sheet with a tensile strength of 780 MPa or more, a region down to 30 μm from a surface of the steel sheet in a sheet thickness direction being defined as a "surface layer part", at the surface layer part of at least one side, particle size 20 nm or more Al oxide grains being present in 3000 to 6000/mm 2 in number density, an average of natural logarithms of the particle sizes of the Al oxide grains measured in μm units being -5.0 to -3.5, a standard error of the natural logarithms of the particle sizes being 0.8 or less, a number of Al oxide grains with deviations of the natural logarithms of the particle sizes from the average of larger than 2 times the standard error being 5% or less of the total number of Al oxide grains with particle sizes of 20 nm or more, a chemical composition at a position of 1/4 of the thickness from the surface of the steel sheet comprising, by mass%, C: 0.050 to 0.800%, Si: 0.01 to 1.20%, Mn: 0.01 to 8.00%, P: 0.100% or less, S: 0.050% or less, Al: 0 to 3.000%, N: 0.010% or less, O: 0 to 0.020%, Cr: 0 to 3.00%, Mo: 0 to 1.00%, B: 0 to 0.0100%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.20%, Cu: 0 to 1.000%, Ni: 0 to 1.000%, and optionally, W: 0 to 0.1%, Ta: 0 to 0.1%, Sn: 0 to 0.05%, Sb: 0 to 0.05%, As: 0 to 0.05%, Mg: 0 to 0.05%, Ca: 0 to 0.05%, Zr: 0 to 0.05%, Y: 0 to 0.05%, La: 0 to 0.05%, Ce: 0 to 0.05%, and other REMs, balance: Fe and impurities, a number density of Al oxide grains at a position of 1/2 of the thickness of the steel sheet being 1000/mm 2 or less, wherein the tensile strength, and the number density and the particle size distribution of the Al oxide grains are measured as defined in the description. a region down to 30 μm from a surface of the steel sheet in a sheet thickness direction being defined as a "surface layer part", at the surface layer part of at least one side, particle size 20 nm or more Al oxide grains being present in 3000 to 6000/mm 2 in number density, an average of natural logarithms of the particle sizes of the Al oxide grains measured in μm units being -5.0 to -3.5, a standard error of the natural logarithms of the particle sizes being 0.8 or less, a number of Al oxide grains with deviations of the natural logarithms of the particle sizes from the average of larger than 2 times the standard error being 5% or less of the total number of Al oxide grains with particle sizes of 20 nm or more, a chemical composition at a position of 1/4 of the thickness from the surface of the steel sheet comprising, by mass%, C: 0.050 to 0.800%, Si: 0.01 to 1.20%, Mn: 0.01 to 8.00%, P: 0.100% or less, S: 0.050% or less, Al: 0 to 3.000%, N: 0.010% or less, O: 0 to 0.020%, Cr: 0 to 3.00%, Mo: 0 to 1.00%, B: 0 to 0.0100%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.20%, Cu: 0 to 1.000%, Ni: 0 to 1.000%, and optionally, W: 0 to 0.1%, Ta: 0 to 0.1%, Sn: 0 to 0.05%, Sb: 0 to 0.05%, As: 0 to 0.05%, Mg: 0 to 0.05%, Ca: 0 to 0.05%, Zr: 0 to 0.05%, Y: 0 to 0.05%, La: 0 to 0.05%, Ce: 0 to 0.05%, and other REMs, balance: Fe and impurities, a number density of Al oxide grains at a position of 1/2 of the thickness of the steel sheet being 1000/mm 2 or less, wherein the tensile strength, and the number density and the particle size distribution of the Al oxide grains are measured as defined in the description.