An electromagnetic stirrer for stirring molten steel of the liquid core in a width-wise direction of the slab includes an iron core disposed with its length-wise axis along a width-wise direction of slab, and a plurality of exciting coils wound around the outer circumference of and about a length-wise axis of the iron core, wherein two-phase or three-phase alternating current is passed through the coils. The phases of the current in the exciting coils are distributed to impart a stirring flow to the molten that includes flow from the minor sides to the center of the slab or from one minor side to the other minor side with a reversing flow at predetermined time intervals.