A secondary cooling method and a secondary cooling device for a casting product casted in a continuous casting machine, the continuous casting machine including, in a secondary cooling zone below a mold, a plurality of pairs of support rolls that support the casting product from both sides of the casting product in a thickness direction, a cooling device being disposed between support rolls adjacent to each other along a casting direction of the continuous casting machine, the cooling device including a coolant pipe that supplies a coolant, and a coolant guide plate with a flat plate shape for spreading the coolant on the casting product, the coolant guide plate being disposed parallel to and spaced in a perpendicular direction from a surface of the casting product.