A continuous casting method of steel in which at least one electromagnetic stirrer (9, 95) is installed at a distance of less than 9 m upstream, in the casting direction, of a reduction rolling position of a slab, and in which a slab with a liquid core is reduced in thickness, characterized in that: the method comprises selectively imparting, by means of the electromagnetic stirrer (9, 95), a stirring flow which causes molten steel to flow from both minor sides of slab toward the width-wise center of slab and collide with each other in the vicinity of the width-wise center, and a stirring flow which causes molten steel to flow from one minor side of slab toward the other minor side thereof while reversing the flowing direction at a predetermined time interval, and in that: the amount of thickness reduction of the slab is adjusted according to the amount of superheat (ΔT) of molten steel in a tundish, and the length, in a width-wise direction of slab, of each of segregation zones with an elements-segregation ratio of from 0.80 to 1.20, which exist in thickness-wise central parts at both width-wise end portions of slab, is set within the range being satisfied by a relationship represented by the following expression: 0 ≤ W ≤ 0.2 × Wo − 2 × d wherein W represents the length, in a width-wise direction of slab, of each of segregation zones existing at both width-wise end portions of the slab (mm), Wo represents the width of the slab (mm), and d represents the thickness of a solidified shell on a minor side of the slab at its reduction rolling position (mm). the method comprises selectively imparting, by means of the electromagnetic stirrer (9, 95), a stirring flow which causes molten steel to flow from both minor sides of slab toward the width-wise center of slab and collide with each other in the vicinity of the width-wise center, and a stirring flow which causes molten steel to flow from one minor side of slab toward the other minor side thereof while reversing the flowing direction at a predetermined time interval, and in that: the amount of thickness reduction of the slab is adjusted according to the amount of superheat (ΔT) of molten steel in a tundish, and the length, in a width-wise direction of slab, of each of segregation zones with an elements-segregation ratio of from 0.80 to 1.20, which exist in thickness-wise central parts at both width-wise end portions of slab, is set within the range being satisfied by a relationship represented by the following expression: 0 ≤ W ≤ 0.2 × Wo − 2 × d wherein W represents the length, in a width-wise direction of slab, of each of segregation zones existing at both width-wise end portions of the slab (mm), Wo represents the width of the slab (mm), and d represents the thickness of a solidified shell on a minor side of the slab at its reduction rolling position (mm). the amount of thickness reduction of the slab is adjusted according to the amount of superheat (ΔT) of molten steel in a tundish, and the length, in a width-wise direction of slab, of each of segregation zones with an elements-segregation ratio of from 0.80 to 1.20, which exist in thickness-wise central parts at both width-wise end portions of slab, is set within the range being satisfied by a relationship represented by the following expression: 0 ≤ W ≤ 0.2 × Wo − 2 × d wherein W represents the length, in a width-wise direction of slab, of each of segregation zones existing at both width-wise end portions of the slab (mm), Wo represents the width of the slab (mm), and d represents the thickness of a solidified shell on a minor side of the slab at its reduction rolling position (mm).