A continuous steel casting method for continuously casting a strand having a thickness of 160 mm to 350 mm, a width of 1600 mm to 2400 mm, and a ratio of the width to the thickness (width/thickness) of 4 to 15, the method comprising: pressing a region of the strand in a soft reduction zone in which a plurality of pairs of strand support rolls that apply pressing force to the strand are disposed, the region of the strand extending from a point at which a strand thickness-wise middle portion has a temperature corresponding to a solid fraction of 0.1 to a point at which a strand thickness-wise middle portion has a temperature corresponding to a flow-limit solid fraction, characterized in that: a thickness of the cast target strand, a reduction rate of the soft reduction zone, and a strand withdrawal speed at which the strand is withdrawn satisfy a relationship expressed by expressions and below: 0.3 / V × α < Z < 1.5 / V × α and α = β × D / Do + γ and in the expressions and, V denotes the strand withdrawal speed (m/min), α denotes a thickness coefficient (dimensionless), Z denotes the reduction rate (mm/m), D denotes a thickness (mm) of the cast target strand at a position immediately below a mold, Do denotes a thickness (mm, Do = 187 mm) of a standard strand at a position immediately below a mold, and β and γ are coefficients determined by a width W (mm) of the cast target strand according to the following ranges of the width W of the strand: β = -0.61 and γ = 1.54 when 1600 ≤ W ≤ 1800; β = -0.60 and γ = 1.57 when 1800 < W ≤ 2000; β = -0.58 and γ = 1.58 when 2000 < W ≤ 2200; and β = -0.53 and γ = 1.54 when 2200 < W ≤ 2400. pressing a region of the strand in a soft reduction zone in which a plurality of pairs of strand support rolls that apply pressing force to the strand are disposed, the region of the strand extending from a point at which a strand thickness-wise middle portion has a temperature corresponding to a solid fraction of 0.1 to a point at which a strand thickness-wise middle portion has a temperature corresponding to a flow-limit solid fraction, a thickness of the cast target strand, a reduction rate of the soft reduction zone, and a strand withdrawal speed at which the strand is withdrawn satisfy a relationship expressed by expressions and below: 0.3 / V × α < Z < 1.5 / V × α and α = β × D / Do + γ and in the expressions and, V denotes the strand withdrawal speed (m/min), α denotes a thickness coefficient (dimensionless), Z denotes the reduction rate (mm/m), D denotes a thickness (mm) of the cast target strand at a position immediately below a mold, Do denotes a thickness (mm, Do = 187 mm) of a standard strand at a position immediately below a mold, and β and γ are coefficients determined by a width W (mm) of the cast target strand according to the following ranges of the width W of the strand: β = -0.61 and γ = 1.54 when 1600 ≤ W ≤ 1800; β = -0.60 and γ = 1.57 when 1800 < W ≤ 2000; β = -0.58 and γ = 1.58 when 2000 < W ≤ 2200; and β = -0.53 and γ = 1.54 when 2200 < W ≤ 2400. V denotes the strand withdrawal speed (m/min), α denotes a thickness coefficient (dimensionless), Z denotes the reduction rate (mm/m), D denotes a thickness (mm) of the cast target strand at a position immediately below a mold, Do denotes a thickness (mm, Do = 187 mm) of a standard strand at a position immediately below a mold, and β and γ are coefficients determined by a width W (mm) of the cast target strand according to the following ranges of the width W of the strand: β = -0.61 and γ = 1.54 when 1600 ≤ W ≤ 1800; β = -0.60 and γ = 1.57 when 1800 < W ≤ 2000; β = -0.58 and γ = 1.58 when 2000 < W ≤ 2200; and β = -0.53 and γ = 1.54 when 2200 < W ≤ 2400. β = -0.61 and γ = 1.54 when 1600 ≤ W ≤ 1800; β = -0.60 and γ = 1.57 when 1800 < W ≤ 2000; β = -0.58 and γ = 1.58 when 2000 < W ≤ 2200; and β = -0.53 and γ = 1.54 when 2200 < W ≤ 2400.