A continuous steel casting method, the method including producing a strand, the producing of the strand including pouring molten steel into a mold for continuous casting and withdrawing a solidified shell from the mold, the solidified shell being a solidified portion of the molten steel, the mold having a pair of mold long sides and a pair of mold short sides with a rectangular interior space being defined within the mold, the method comprising applying an AC magnetic field to in-mold molten steel via AC magnetic field generation devices, thereby creating, via the AC magnetic field, a horizontal swirling and stirring flow in the in-mold molten steel, each of the AC magnetic field generation devices being placed on a back surface of a corresponding one of the pair of mold long sides, the AC magnetic field generation devices facing each other with the mold long sides being positioned therebetween, wherein a spacing between the mold long sides that face each other is 200 to 300 mm, a submerged entry nozzle has two discharge ports for pouring molten steel into the interior space, each of the discharge ports having a discharge angle within a range of 5° in a downward direction to 50° in a downward direction, the AC magnetic field has a frequency of 0.5 Hz or greater and 3.0 Hz or less, and in accordance with a location of a peak of the AC magnetic field, a submergence depth of the submerged entry nozzle, the submergence depth being a distance from the surface of the in-mold molten steel to an upper end of the discharge ports of the submerged entry nozzle, and a magnetic flux density at the location of the peak of the AC magnetic field generated by the AC magnetic field generation devices are determined to satisfy one of three types of conditions described below, namely conditions, conditions, and conditions, conditions: when the distance from the surface of the in-mold molten steel to the location of the peak of the AC magnetic field is 200 mm or greater and less than 300 mm, the submergence depth of the submerged entry nozzle is 100 mm or greater and less than 200 mm, and the magnetic flux density at the location of the peak of the AC magnetic field is 0.040 T or greater and less than 0.060 T, conditions: when the distance from the surface of the in-mold molten steel to the location of the peak of the AC magnetic field is 300 mm or greater and less than 400 mm, the submergence depth of the submerged entry nozzle is 100 mm or greater and less than 300 mm, and the magnetic flux density at the location of the peak of the AC magnetic field is 0.060 T or greater and less than 0.080 T, and conditions: when the distance from the surface of the in-mold molten steel to the location of the peak of the AC magnetic field is 400 mm or greater and less than 500 mm, the submergence depth of the submerged entry nozzle is 100 mm or greater and less than 300 mm, and the magnetic flux density at the location of the peak of the AC magnetic field is 0.080 T or greater and less than 0.100 T. the method comprising applying an AC magnetic field to in-mold molten steel via AC magnetic field generation devices, thereby creating, via the AC magnetic field, a horizontal swirling and stirring flow in the in-mold molten steel, each of the AC magnetic field generation devices being placed on a back surface of a corresponding one of the pair of mold long sides, the AC magnetic field generation devices facing each other with the mold long sides being positioned therebetween, wherein a spacing between the mold long sides that face each other is 200 to 300 mm, a submerged entry nozzle has two discharge ports for pouring molten steel into the interior space, each of the discharge ports having a discharge angle within a range of 5° in a downward direction to 50° in a downward direction, the AC magnetic field has a frequency of 0.5 Hz or greater and 3.0 Hz or less, and in accordance with a location of a peak of the AC magnetic field, a submergence depth of the submerged entry nozzle, the submergence depth being a distance from the surface of the in-mold molten steel to an upper end of the discharge ports of the submerged entry nozzle, and a magnetic flux density at the location of the peak of the AC magnetic field generated by the AC magnetic field generation devices are determined to satisfy one of three types of conditions described below, namely conditions, conditions, and conditions, conditions: when the distance from the surface of the in-mold molten steel to the location of the peak of the AC magnetic field is 200 mm or greater and less than 300 mm, the submergence depth of the submerged entry nozzle is 100 mm or greater and less than 200 mm, and the magnetic flux density at the location of the peak of the AC magnetic field is 0.040 T or greater and less than 0.060 T, conditions: when the distance from the surface of the in-mold molten steel to the location of the peak of the AC magnetic field is 300 mm or greater and less than 400 mm, the submergence depth of the submerged entry nozzle is 100 mm or greater and less than 300 mm, and the magnetic flux density at the location of the peak of the AC magnetic field is 0.060 T or greater and less than 0.080 T, and conditions: when the distance from the surface of the in-mold molten steel to the location of the peak of the AC magnetic field is 400 mm or greater and less than 500 mm, the submergence depth of the submerged entry nozzle is 100 mm or greater and less than 300 mm, and the magnetic flux density at the location of the peak of the AC magnetic field is 0.080 T or greater and less than 0.100 T.