A high-strength steel sheet having: a chemical composition containing, by mass%, C: 0.05% to 0.15%, Si: 0.010% to 1.80%, Mn: 1.8% to 3.2%, P: 0.05% or less, S: 0.02% or less, Al: 0.01% to 2.0%, one or more of B: 0.0001% to 0.005%, Ti: 0.005% to 0.04%, and Mo: 0.03% to 0.50%, optionally Cr: 1.0% or less and/or one or more of Cu, Ni, Sn, As, Sb, Ca, Mg, Pb, Co, Ta, W, REM, Zn, Nb, V, Cs, and Hf of 1% or less in total, and the balance being Fe and inevitable impurities, a microstructure, where observed in a cross section in a thickness direction perpendicular to a rolling direction, including a martensite phase having a volume fraction of 50% to 80%, and a ferrite phase having an average grain diameter of 3 μm or more and 13 μm or less, wherein a volume fraction of ferrite grains having an aspect ratio of 2.0 or less with respect to the whole ferrite phase is 70% or more, and wherein an average length in a longitudinal direction in a width direction of the steel sheet of the ferrite grains is 20 μm or less, and a yield strength (YP) of 550 MPa or more, wherein the average grain diameter of a ferrite phase is determined by etching a portion located at 1⁄4 of the thickness from the surface in a cross section perpendicular to the rolling direction with a 1% nital solution to expose the microstructure, by taking photographs in 10 fields of view by using a scanning electron microscope (SEM) at a magnification of 1000 times, and by using a cutting method in accordance with ASTM E 112-10, and the aspect ratio of ferrite grains is determined by etching a portion located at 1⁄4 of the thickness from the surface in a cross section perpendicular to the rolling direction with a 1% natal solution to expose the microstructure, by taking photographs in 10 fields of view by using a scanning electron microscope (SEM) at a magnification of 1000 times, and by calculating the ratio of the length in the width direction to the length in the thickness direction as an aspect ratio. a chemical composition containing, by mass%, C: 0.05% to 0.15%, Si: 0.010% to 1.80%, Mn: 1.8% to 3.2%, P: 0.05% or less, S: 0.02% or less, Al: 0.01% to 2.0%, one or more of B: 0.0001% to 0.005%, Ti: 0.005% to 0.04%, and Mo: 0.03% to 0.50%, optionally Cr: 1.0% or less and/or one or more of Cu, Ni, Sn, As, Sb, Ca, Mg, Pb, Co, Ta, W, REM, Zn, Nb, V, Cs, and Hf of 1% or less in total, and the balance being Fe and inevitable impurities, a microstructure, where observed in a cross section in a thickness direction perpendicular to a rolling direction, including a martensite phase having a volume fraction of 50% to 80%, and a ferrite phase having an average grain diameter of 3 μm or more and 13 μm or less, wherein a volume fraction of ferrite grains having an aspect ratio of 2.0 or less with respect to the whole ferrite phase is 70% or more, and wherein an average length in a longitudinal direction in a width direction of the steel sheet of the ferrite grains is 20 μm or less, and a yield strength (YP) of 550 MPa or more, wherein the average grain diameter of a ferrite phase is determined by etching a portion located at 1⁄4 of the thickness from the surface in a cross section perpendicular to the rolling direction with a 1% nital solution to expose the microstructure, by taking photographs in 10 fields of view by using a scanning electron microscope (SEM) at a magnification of 1000 times, and by using a cutting method in accordance with ASTM E 112-10, and the aspect ratio of ferrite grains is determined by etching a portion located at 1⁄4 of the thickness from the surface in a cross section perpendicular to the rolling direction with a 1% natal solution to expose the microstructure, by taking photographs in 10 fields of view by using a scanning electron microscope (SEM) at a magnification of 1000 times, and by calculating the ratio of the length in the width direction to the length in the thickness direction as an aspect ratio. <EOS>