A slab continuous casting apparatus according to this invention is configured to supply molten metal from a tundish to a slab water-cooled mold through at least an upper nozzle, a stopper, and an immersion nozzle and solidify the molten metal, and is provided with an immersion nozzle quick replacement mechanism. The slab continuous casting apparatus includes a discharge direction change mechanism that is provided between the stopper and the immersion nozzle and is capable of freely changing a discharge angle of the molten metal in a horizontal cross-section during casting.