A high-strength steel sheet comprising, as component composition, by mass: C: 0.15 to 0.35%; total of Si and Al: 0.5 to 2.5%; Mn: 1.0 to 4.0%; P: more than 0% and 0.05% or less; S: more than 0% and 0.01% or less; and optionally at least any one of following (a) to (c): (a) at least one selected from the group consisting of Cu, Ni, Mo, Cr and B in a total amount of more than 0% and 1.0% or less; (b) at least one selected from the group consisting of V, Nb, Ti, Zr and Hf in a total amount of more than 0% and 0.2% or less; and (c) at least one selected from the group consisting of Ca, Mg and REM in a total amount of more than 0% and 0.01% or less, with the balance being Fe and inevitable impurities, wherein a steel structure satisfies, in ratio with respect to the whole structure: ferrite: more than 5 area% and 50 area% or less; total of tempered martensite and bainite: 30 area% or more; and retained austenite: 10 volume% or more, the steel structure further includes martensite-austenite constituent and the steel structure satisfies: an average circle equivalent diameter of the martensite-austenite constituent 1.0 μm or less; an average circle equivalent diameter of the retained austenite: 1.0 μm or less; all the microstructure features are measured according to the method described in the description; and a volume ratio of retained austenite with a circle equivalent diameter of 1.5 μm or more to the whole retained austenite: 5% or more. C: 0.15 to 0.35%; total of Si and Al: 0.5 to 2.5%; Mn: 1.0 to 4.0%; P: more than 0% and 0.05% or less; S: more than 0% and 0.01% or less; and optionally at least any one of following (a) to (c): (a) at least one selected from the group consisting of Cu, Ni, Mo, Cr and B in a total amount of more than 0% and 1.0% or less; (b) at least one selected from the group consisting of V, Nb, Ti, Zr and Hf in a total amount of more than 0% and 0.2% or less; and (c) at least one selected from the group consisting of Ca, Mg and REM in a total amount of more than 0% and 0.01% or less, with the balance being Fe and inevitable impurities, wherein (a) at least one selected from the group consisting of Cu, Ni, Mo, Cr and B in a total amount of more than 0% and 1.0% or less; (b) at least one selected from the group consisting of V, Nb, Ti, Zr and Hf in a total amount of more than 0% and 0.2% or less; and (c) at least one selected from the group consisting of Ca, Mg and REM in a total amount of more than 0% and 0.01% or less, with the balance being Fe and inevitable impurities, wherein ferrite: more than 5 area% and 50 area% or less; total of tempered martensite and bainite: 30 area% or more; and retained austenite: 10 volume% or more, the steel structure further includes martensite-austenite constituent and the steel structure satisfies: an average circle equivalent diameter of the martensite-austenite constituent 1.0 μm or less; an average circle equivalent diameter of the retained austenite: 1.0 μm or less; all the microstructure features are measured according to the method described in the description; and a volume ratio of retained austenite with a circle equivalent diameter of 1.5 μm or more to the whole retained austenite: 5% or more. an average circle equivalent diameter of the martensite-austenite constituent 1.0 μm or less; an average circle equivalent diameter of the retained austenite: 1.0 μm or less; all the microstructure features are measured according to the method described in the description; and a volume ratio of retained austenite with a circle equivalent diameter of 1.5 μm or more to the whole retained austenite: 5% or more.