A thin high-strength cold-rolled steel sheet having a thickness of 5 mm or less, comprising: a composition containing, by mass, C: 0.25% or more and 0.45% or less, Si: 0.50% to 2.50%, Mn: 2.00% or more and less than 3.50%, P: 0.001% to 0.100%, S: 0.0200% or less, N: 0.0100% or less, Al: 0.01% to 0.100%, one or two elements selected from Ti: 0.005% to 0.100% and Nb: 0.005% to 0.100%, optionally one or more groups selected from Groups A to D below: Group A: one or more elements selected from B: 0.0001% to 0.0050%, Cr: 0.05% to 1.00%, and Cu: 0.05% to 1.00% Group B: one or two elements selected from Sb: 0.002% to 0.200% and Sn: 0.002% to 0.200% Group C: Ta: 0.001% to 0.100% Group D: one or more elements selected from Ca: 0.0005% to 0.0050%, Mg: 0.0005% to 0.0050%, and REM: 0.0005% to 0.0050%, the balance being Fe and inevitable impurities, and a microstructure including, by volume, 15% or more and 70% or less ferrite phase and 20% or more and 40% or less retained austenite phase, the balance being 30% or less (not including 0%) martensite phase or including 30% or less (not including 0%) martensite phase and 10% or less (including 0%) pearlite phase and/or carbide, wherein crystal grains of the retained austenite phase have an average diameter of 2.0 μm or less and an aspect ratio of 2.0 or more, a tensile strength of the thin high-strength cold-rolled steel sheet is 980 MPa or more, an in-plane anisotropy δTS of the thin high-strength cold-rolled steel sheet in terms of tensile strength defined by Formula below is 25 MPa or less, and an in-plane anisotropy δEl of the thin high-strength cold-rolled steel sheet in terms of total elongation defined by Formula below is 10% or less: δTS = TS L + TS C − 2 × TS D / 2 where δTS: in-plane anisotropy (MPa) in terms of tensile strength TS, TS L: tensile strength (MPa) in a direction parallel to the rolling direction (L direction), TS C: tensile strength (MPa) in a direction (C direction) perpendicular to the rolling direction, and TS D: tensile strength (MPa) in a direction (D direction) inclined at an angle of 45° with respect to the rolling direction, δEl = El L + El C − 2 × El D / 2 where δEl: in-plane anisotropy (%) in terms of total elongation El, El L: total elongation (%) in a direction parallel to the rolling direction (L direction), El C: total elongation (%) in a direction (C direction) perpendicular to the rolling direction, and El D: total elongation (%) in a direction (D direction) inclined at an angle of 45° with respect to the rolling direction. a composition containing, by mass, C: 0.25% or more and 0.45% or less, Si: 0.50% to 2.50%, Mn: 2.00% or more and less than 3.50%, P: 0.001% to 0.100%, S: 0.0200% or less, N: 0.0100% or less, Al: 0.01% to 0.100%, one or two elements selected from Ti: 0.005% to 0.100% and Nb: 0.005% to 0.100%, optionally one or more groups selected from Groups A to D below: Group A: one or more elements selected from B: 0.0001% to 0.0050%, Cr: 0.05% to 1.00%, and Cu: 0.05% to 1.00% Group B: one or two elements selected from Sb: 0.002% to 0.200% and Sn: 0.002% to 0.200% Group C: Ta: 0.001% to 0.100% Group D: one or more elements selected from Ca: 0.0005% to 0.0050%, Mg: 0.0005% to 0.0050%, and REM: 0.0005% to 0.0050%, the balance being Fe and inevitable impurities, and Group A: one or more elements selected from B: 0.0001% to 0.0050%, Cr: 0.05% to 1.00%, and Cu: 0.05% to 1.00% Group B: one or two elements selected from Sb: 0.002% to 0.200% and Sn: 0.002% to 0.200% Group C: Ta: 0.001% to 0.100% Group D: one or more elements selected from Ca: 0.0005% to 0.0050%, Mg: 0.0005% to 0.0050%, and REM: 0.0005% to 0.0050%, the balance being Fe and inevitable impurities, and a microstructure including, by volume, 15% or more and 70% or less ferrite phase and 20% or more and 40% or less retained austenite phase, the balance being 30% or less (not including 0%) martensite phase or including 30% or less (not including 0%) martensite phase and 10% or less (including 0%) pearlite phase and/or carbide, wherein crystal grains of the retained austenite phase have an average diameter of 2.0 μm or less and an aspect ratio of 2.0 or more, a tensile strength of the thin high-strength cold-rolled steel sheet is 980 MPa or more, an in-plane anisotropy δTS of the thin high-strength cold-rolled steel sheet in terms of tensile strength defined by Formula below is 25 MPa or less, and an in-plane anisotropy δEl of the thin high-strength cold-rolled steel sheet in terms of total elongation defined by Formula below is 10% or less: δTS = TS L + TS C − 2 × TS D / 2 where δTS: in-plane anisotropy (MPa) in terms of tensile strength TS, TS L: tensile strength (MPa) in a direction parallel to the rolling direction (L direction), TS C: tensile strength (MPa) in a direction (C direction) perpendicular to the rolling direction, and TS D: tensile strength (MPa) in a direction (D direction) inclined at an angle of 45° with respect to the rolling direction, δEl = El L + El C − 2 × El D / 2 where δEl: in-plane anisotropy (%) in terms of total elongation El, El L: total elongation (%) in a direction parallel to the rolling direction (L direction), El C: total elongation (%) in a direction (C direction) perpendicular to the rolling direction, and El D: total elongation (%) in a direction (D direction) inclined at an angle of 45° with respect to the rolling direction.