A high-strength steel sheet, comprising: a chemical composition represented by, in mass%, C: 0.075 to 0.400%, Si: 0.01 to 2.50%, Mn: 0.50 to 3.50%, P: 0.1000% or less, S: 0.0100% or less, Al: 2.000% or less, N: 0.0100% or less, O: 0.0100% or less, Ti: 0.000 to 0.200%, Nb: 0.000 to 0.100%, V: 0.000 to 0.500%, Cr: 0.00 to 2.00%, Ni: 0.00 to 2.00%, Cu: 0.00 to 2.00%, Mo: 0.00 to 1.00%, B: 0.0000 to 0.0100%, W: 0.00 to 2.00%, one type or two types or more selected from the group consisting of Ca, Ce, Mg, Zr, La, and REM: 0.0000 to 0.0100% in total, a balance: Fe and impurities, and a parameter Q0 expressed by Expression 1: 0.35 or more; and a microstructure represented by, in a 1/8 thickness to 3/8 thickness range with 1/4 thickness of a sheet thickness from a surface being a middle, in volume fraction, ferrite: 85% or less, bainite: 3% or more and 95% or less, tempered martensite: 1% or more and 80% or less, retained austenite: 1% or more and 25% or less, pearlite and coarse cementite: 5% or less in total, and fresh martensite: 5% or less, wherein a solid-solution carbon content in the retained austenite is 0.70 to 1.30 mass%, and in all grain boundaries of retained austenite grains having an aspect ratio of 2.50 or less and a circle-equivalent diameter of 0.80 μm or more, a proportion of interfaces with the tempered martensite or the fresh martensite is 75% or less, Q 0 = Si + 0.1 Mn + 0.6 A 1 wherein Si, Mn, and Al are set to the contents of the respective elements in mass%, wherein the volume fraction, the solid-solution carbon content, the aspect ratio, the circle-equivalent diameter and the proportion of interfaces with the tempered martensite or the fresh martensite are measured as disclosed in the description. a chemical composition represented by, in mass%, C: 0.075 to 0.400%, Si: 0.01 to 2.50%, Mn: 0.50 to 3.50%, P: 0.1000% or less, S: 0.0100% or less, Al: 2.000% or less, N: 0.0100% or less, O: 0.0100% or less, Ti: 0.000 to 0.200%, Nb: 0.000 to 0.100%, V: 0.000 to 0.500%, Cr: 0.00 to 2.00%, Ni: 0.00 to 2.00%, Cu: 0.00 to 2.00%, Mo: 0.00 to 1.00%, B: 0.0000 to 0.0100%, W: 0.00 to 2.00%, one type or two types or more selected from the group consisting of Ca, Ce, Mg, Zr, La, and REM: 0.0000 to 0.0100% in total, a balance: Fe and impurities, and a parameter Q0 expressed by Expression 1: 0.35 or more; and a microstructure represented by, in a 1/8 thickness to 3/8 thickness range with 1/4 thickness of a sheet thickness from a surface being a middle, in volume fraction, ferrite: 85% or less, bainite: 3% or more and 95% or less, tempered martensite: 1% or more and 80% or less, retained austenite: 1% or more and 25% or less, pearlite and coarse cementite: 5% or less in total, and fresh martensite: 5% or less, wherein a solid-solution carbon content in the retained austenite is 0.70 to 1.30 mass%, and in all grain boundaries of retained austenite grains having an aspect ratio of 2.50 or less and a circle-equivalent diameter of 0.80 μm or more, a proportion of interfaces with the tempered martensite or the fresh martensite is 75% or less, Q 0 = Si + 0.1 Mn + 0.6 A 1 wherein Si, Mn, and Al are set to the contents of the respective elements in mass%, wherein the volume fraction, the solid-solution carbon content, the aspect ratio, the circle-equivalent diameter and the proportion of interfaces with the tempered martensite or the fresh martensite are measured as disclosed in the description. wherein Si, Mn, and Al are set to the contents of the respective elements in mass%, wherein the volume fraction, the solid-solution carbon content, the aspect ratio, the circle-equivalent diameter and the proportion of interfaces with the tempered martensite or the fresh martensite are measured as disclosed in the description. <EOS>