A continuous casting method of steel in which a slab having a rectangular cross section is cast while causing vibration in the slab with liquid core by disposing at least one pair of impact-vibration equipments on both short side surfaces of slab and continuously impacting those surfaces, characterized in that: a vibration energy, a distance between shafts of adjacent guide rolls and a liquid core thickness are adjusted, so that the impacting of the short side surface causes a curve of displacement δ(x) of the long side slab surface in a slab thickness-wise direction as defined by the following formulas and to intersect a straight line δ(x) = 0.10 mm at two locations, and a distance of the intersection farther away from the coordinate origin in a slab width-wise direction, representing the distance from an impact position at the short side of the slab, is at least 200 mm; and the short side is impacted, δ x = exp − 1.5 × ln x / 200 × ΔR / Δ R 0 0.587 2 × δmax δmax = L 0 × E / E 0 0.5 × ΔR / Δ R 0 × t / t 0 0.446 where each symbol in formulas and designates as follows, x is a distance (mm) in a slab width-wise direction with the impact position on the short side of slab being 0, δ(x) is a displacement (mm) of slab surface in a slab thickness-wise direction at the position x, δmax is the maximum displacement (mm) in a slab thickness-wise direction, ΔR is a distance between shafts of adjacent guide rolls (mm) at the position where impacting the short side, E is impact energy per side per segment, and t is a liquid core thickness of the slab at the impact position on the short side of the slab (mm), wherein Constants are defined as E 0 = 39, ΔR 0 = 245 (mm), t 0 = 26 (mm), and L 0 = 0.114 (mm). a vibration energy, a distance between shafts of adjacent guide rolls and a liquid core thickness are adjusted, so that the impacting of the short side surface causes a curve of displacement δ(x) of the long side slab surface in a slab thickness-wise direction as defined by the following formulas and to intersect a straight line δ(x) = 0.10 mm at two locations, and a distance of the intersection farther away from the coordinate origin in a slab width-wise direction, representing the distance from an impact position at the short side of the slab, is at least 200 mm; and the short side is impacted, δ x = exp − 1.5 × ln x / 200 × ΔR / Δ R 0 0.587 2 × δmax δmax = L 0 × E / E 0 0.5 × ΔR / Δ R 0 × t / t 0 0.446 where each symbol in formulas and designates as follows, x is a distance (mm) in a slab width-wise direction with the impact position on the short side of slab being 0, δ(x) is a displacement (mm) of slab surface in a slab thickness-wise direction at the position x, δmax is the maximum displacement (mm) in a slab thickness-wise direction, ΔR is a distance between shafts of adjacent guide rolls (mm) at the position where impacting the short side, E is impact energy per side per segment, and t is a liquid core thickness of the slab at the impact position on the short side of the slab (mm), wherein Constants are defined as E 0 = 39, ΔR 0 = 245 (mm), t 0 = 26 (mm), and L 0 = 0.114 (mm). x is a distance (mm) in a slab width-wise direction with the impact position on the short side of slab being 0, δ(x) is a displacement (mm) of slab surface in a slab thickness-wise direction at the position x, δmax is the maximum displacement (mm) in a slab thickness-wise direction, ΔR is a distance between shafts of adjacent guide rolls (mm) at the position where impacting the short side, E is impact energy per side per segment, and t is a liquid core thickness of the slab at the impact position on the short side of the slab (mm), wherein Constants are defined as E 0 = 39, ΔR 0 = 245 (mm), t 0 = 26 (mm), and L 0 = 0.114 (mm).