A steel sheet comprising: a base iron; a scale of 10.0 μm or less in thickness on a surface of the base iron; and a subscale between the base iron and the scale, wherein the base iron comprises a chemical composition represented by, in mass%, C: 0.05% to 0.20%, Si: 0.01% to 1.50%, Mn: 1.50% to 2.50%, P: 0.05% or less, S: 0.03% or less, Al: 0.005% to 0.10%, N: 0.008% or less, Cr: 0.30% to 1.00%, Ti: 0.06% to 0.20%, Nb: 0.00% to 0.10%, V: 0.00% to 0.20%, B: 0.0000% to 0.0050%, Cu: 0.00% to 0.50%, Ni: 0.00% to 0.50%, Mo: 0.00% to 0.50%, W: 0.00% to 0.50%, Ca: 0.0000% to 0.0050%, Mg: 0.0000% to 0.0050%, REM: 0.000% to 0.010%, and the balance: Fe and impurities, wherein, in the subscale, an average value of Cr concentrations is 1.50 mass% to 5.00 mass%, wherein the average value of the Cr concentrations is determined by defining a measurement region as a region made of 10 measurement points continually lining up in the rolling direction with an interval between the measurement points being 0.1 μm, so that a dimension in the rolling direction of the measurement region is 1 μm; a length in the rolling direction of an object region of the mapping of the Cr concentrations is 50 μm or more, so that there are 50 or more measurement regions; finding an average value and a maximum value Cmax of the Cr concentrations for every measurement region; calculating an average value Ave of the maximum values Cmax among the 50 or more measurement regions; and defining the average value Ave as an average value of the Cr concentrations in the subscale; and one part or more exist(s) where a ratio of one's maximum value Cmax to other's maximum value Cmax is 0.90 or less or 1.11 or more between two adjacent measurement regions among the 50 or more measurement regions, wherein, in the steel sheet, a percentage of an amount of Ti contained in carbide or carbonitride of 100 nm or more and 1 μm or less in grain diameter to a parameter Ti eff represented by a following formula 1 is 30% or less, [Ti] denoting a Ti content in mass% and denoting a N content in mass% in the following formula 1, Ti eff = Ti − 48 / 14 N and a yield strength in the rolling direction is 700 MPa or more and less than 800 MPa and that a yield ratio is 85% or more, wherein the yield strength and the yield ratio is measured by a tensile test in accordance with JIS Z2241 at a room temperature. a base iron; a scale of 10.0 μm or less in thickness on a surface of the base iron; and a subscale between the base iron and the scale, wherein the base iron comprises a chemical composition represented by, in mass%, C: 0.05% to 0.20%, Si: 0.01% to 1.50%, Mn: 1.50% to 2.50%, P: 0.05% or less, S: 0.03% or less, Al: 0.005% to 0.10%, N: 0.008% or less, Cr: 0.30% to 1.00%, Ti: 0.06% to 0.20%, Nb: 0.00% to 0.10%, V: 0.00% to 0.20%, B: 0.0000% to 0.0050%, Cu: 0.00% to 0.50%, Ni: 0.00% to 0.50%, Mo: 0.00% to 0.50%, W: 0.00% to 0.50%, Ca: 0.0000% to 0.0050%, Mg: 0.0000% to 0.0050%, REM: 0.000% to 0.010%, and the balance: Fe and impurities, wherein, in the subscale, an average value of Cr concentrations is 1.50 mass% to 5.00 mass%, wherein the average value of the Cr concentrations is determined by defining a measurement region as a region made of 10 measurement points continually lining up in the rolling direction with an interval between the measurement points being 0.1 μm, so that a dimension in the rolling direction of the measurement region is 1 μm; a length in the rolling direction of an object region of the mapping of the Cr concentrations is 50 μm or more, so that there are 50 or more measurement regions; finding an average value and a maximum value Cmax of the Cr concentrations for every measurement region; calculating an average value Ave of the maximum values Cmax among the 50 or more measurement regions; and defining the average value Ave as an average value of the Cr concentrations in the subscale; and one part or more exist(s) where a ratio of one's maximum value Cmax to other's maximum value Cmax is 0.90 or less or 1.11 or more between two adjacent measurement regions among the 50 or more measurement regions, wherein, in the steel sheet, a percentage of an amount of Ti contained in carbide or carbonitride of 100 nm or more and 1 μm or less in grain diameter to a parameter Ti eff represented by a following formula 1 is 30% or less, [Ti] denoting a Ti content in mass% and denoting a N content in mass% in the following formula 1, Ti eff = Ti − 48 / 14 N and a yield strength in the rolling direction is 700 MPa or more and less than 800 MPa and that a yield ratio is 85% or more, wherein the yield strength and the yield ratio is measured by a tensile test in accordance with JIS Z2241 at a room temperature.