A high-strength steel sheet with tensile strength of 590 MPa or more measured in accordance with JIS Z 2241 as defined in the description, the high-strength steel sheet comprising a chemical composition comprising: by mass%, C in a range from 0.080 to 0.500%; Si of 2.50% or less; Mn in a range from 0.50 to 5.00%; P of 0.100% or less; S of 0.0100% or less; Al in a range from 0.001 to 2.000%; N of 0.0150% or less; O of 0.0050% or less; optionally one or more of Ti of 0.300% or less, Nb of 0.100% or less, and V of 1.00% or less; optionally one or more of Cr of 2.00% or less, Ni of 2.00% or less, Cu of 2.00% or less, Mo of 1.00% or less, W of 1.00% or less, and B of 0.0100% or less; optionally one or more of Sn of 1.00% or less, and Sb of 0.200% or less; optionally one or more of Ca, Ce, Mg, Zr, La, Hf, and REM being 0.0100% or less in total; and the balance consisting of Fe and inevitable impurities, and in a steel sheet satisfying a formula, the high-strength steel sheet comprising a microstructure in a region from 1/8t to 3/8t from a steel sheet surface, wherein t is the sheet thickness, the microstructure comprising: by volume%, 20% or more of acicular ferrite; 20% or more of an island-shaped hard structure comprising one or more of martensite, tempered martensite, and residual austenite, 2% to 25% of the residual austenite; 20% or less of aggregated ferrite; and 5% or less of pearlite and/or cementite in total, wherein in the island-shaped hard structure, an average aspect ratio of a hard region having an equivalent circle diameter of 1.5 μm or more is 2.0 or more, and an average aspect ratio of a hard region having an equivalent circle diameter of less than 1.5 μm is less than 2.0, and an average of a number density per unit area (hereinafter also simply referred to as "the number density") of the hard region having the equivalent circle diameter of less than 1.5 μm is equal to or more than 1.0 × 10 10 pieces·m -2, and when the number density of the island-shaped hard structure in an area of at least 5.0 × 10 -10 m 2 in each of three view fields is obtained, a ratio between a maximum number density and a minimum number density thereof is 2.5 or less, Si + 0.35 Mn + 0.15 Al + 2.80 Cr + 0.84 Mo + 0.50 Nb + 0.30 Ti ≥ 1.00 [element]: mass% of each element. C in a range from 0.080 to 0.500%; Si of 2.50% or less; Mn in a range from 0.50 to 5.00%; P of 0.100% or less; S of 0.0100% or less; Al in a range from 0.001 to 2.000%; N of 0.0150% or less; O of 0.0050% or less; optionally one or more of Ti of 0.300% or less, Nb of 0.100% or less, and V of 1.00% or less; optionally one or more of Cr of 2.00% or less, Ni of 2.00% or less, Cu of 2.00% or less, Mo of 1.00% or less, W of 1.00% or less, and B of 0.0100% or less; optionally one or more of Sn of 1.00% or less, and Sb of 0.200% or less; optionally one or more of Ca, Ce, Mg, Zr, La, Hf, and REM being 0.0100% or less in total; and the balance consisting of Fe and inevitable impurities, and in a steel sheet satisfying a formula, the high-strength steel sheet comprising a microstructure in a region from 1/8t to 3/8t from a steel sheet surface, wherein t is the sheet thickness, the microstructure comprising: by volume%, 20% or more of acicular ferrite; 20% or more of an island-shaped hard structure comprising one or more of martensite, tempered martensite, and residual austenite, 2% to 25% of the residual austenite; 20% or less of aggregated ferrite; and 5% or less of pearlite and/or cementite in total, wherein in the island-shaped hard structure, an average aspect ratio of a hard region having an equivalent circle diameter of 1.5 μm or more is 2.0 or more, and an average aspect ratio of a hard region having an equivalent circle diameter of less than 1.5 μm is less than 2.0, and an average of a number density per unit area (hereinafter also simply referred to as "the number density") of the hard region having the equivalent circle diameter of less than 1.5 μm is equal to or more than 1.0 × 10 10 pieces·m -2, and when the number density of the island-shaped hard structure in an area of at least 5.0 × 10 -10 m 2 in each of three view fields is obtained, a ratio between a maximum number density and a minimum number density thereof is 2.5 or less, Si + 0.35 Mn + 0.15 Al + 2.80 Cr + 0.84 Mo + 0.50 Nb + 0.30 Ti ≥ 1.00 [element]: mass% of each element.