A high-strength steel sheet comprising: a chemical composition containing, in mass%, C: 0.05% to 0.20%, Si: 0.30% to 2.50%, Mn: 1.50% to 3.40%, P: 0.001% to 0.100%, S: 0.0001% to 0.0200%, Al: 0.010% to 1.000%, N: 0.0005% to 0.0100%, Nb: 0.01% to 0.100%, optionally, in mass%, at least one or more elements selected from Ti: 0.100% or less, V: 0.100% or less, B: 0.0100% or less, Mo: 0.50% or less, Cr: 1.00% or less, Cu: 1.00% or less, Ni: 0.50% or less, As: 0.500% or less, Sb: 0.200% or less, Sn: 0.200% or less, Ta: 0.100% or less, Ca: 0.0200% or less, Mg: 0.0200% or less, Zn: 0.020% or less, Co: 0.020% or less, Zr: 0.020% or less, and REMs: 0.0200% or less, and the balance being Fe and incidental impurities; and a steel structure that contains ferrite and a harder phase and in which the ferrite accounts for 30% to 70% in terms of area ratio, and the harder phase contains bainitic ferrite, tempered martensite, martensite (including 0%), and retained austenite (including 0%), wherein a maximum grain diameter of ferrite d max is 2.5 um or less, an area ratio of ferrite A F and an average grain diameter of ferrite d F satisfy A F [%]/d F [μm] ≥ 15, a tensile strength TS of 980 MPa or more, a TS × El of 17000 MPa·% or more, and a TS variation ΔTS = the maximum TS - the minimum TS of less than 45 MPa, whereas the TS, the TS × El and the ΔTS are measured with the methods disclosed in the description, and whereas the area ratio of ferrite A F, the area ratio of the harder phase, the average grain diameter of ferrite d F and the maximum grain diameter of ferrite d max are measured with the methods disclosed in the description. C: 0.05% to 0.20%, Si: 0.30% to 2.50%, Mn: 1.50% to 3.40%, P: 0.001% to 0.100%, S: 0.0001% to 0.0200%, Al: 0.010% to 1.000%, N: 0.0005% to 0.0100%, Nb: 0.01% to 0.100%, optionally, in mass%, at least one or more elements selected from Ti: 0.100% or less, V: 0.100% or less, B: 0.0100% or less, Mo: 0.50% or less, Cr: 1.00% or less, Cu: 1.00% or less, Ni: 0.50% or less, As: 0.500% or less, Sb: 0.200% or less, Sn: 0.200% or less, Ta: 0.100% or less, Ca: 0.0200% or less, Mg: 0.0200% or less, Zn: 0.020% or less, Co: 0.020% or less, Zr: 0.020% or less, and REMs: 0.0200% or less, and the balance being Fe and incidental impurities; and a steel structure that contains ferrite and a harder phase and in which the ferrite accounts for 30% to 70% in terms of area ratio, and the harder phase contains bainitic ferrite, tempered martensite, martensite (including 0%), and retained austenite (including 0%), wherein a maximum grain diameter of ferrite d max is 2.5 um or less, an area ratio of ferrite A F and an average grain diameter of ferrite d F satisfy A F [%]/d F [μm] ≥ 15, a tensile strength TS of 980 MPa or more, a TS × El of 17000 MPa·% or more, and a TS variation ΔTS = the maximum TS - the minimum TS of less than 45 MPa, whereas the TS, the TS × El and the ΔTS are measured with the methods disclosed in the description, and whereas the area ratio of ferrite A F, the area ratio of the harder phase, the average grain diameter of ferrite d F and the maximum grain diameter of ferrite d max are measured with the methods disclosed in the description.