PURPOSE: To cast a vertically short steel ingot which is free from central segregation, porosity and surface crack by evenly providing recesses at a specific area ratio to the base of a casting mold in the stage of casting said ingot by the casting mold which is short in the vertical length.

CONSTITUTION: A gate 4 is disposed in the slow cooling casting mold 2 which is of a horizontal moving type and has a low height and large inside area. The molten steel in a tundish 1 is cast from a tundish nozzle 3 into the casging mold. The molten steel is cast in this stage while the casting space S is increased by horizontally moving the mold 2 in an arrow direction and moving the gate 4 toward the right in the mold 2. The molten steel in the mold 2 is solidified in one direction upward from the base. V-shaped vertical and horizontal grooves 5A, 5B are formed to a grid shape to the base 2A of the mold 2 to be used and the recesses 5 by these grooves are evenly formed to the base 2A so as to occupy 50W70% of the bottom area. The unevenness of heat extraction is eliminated by the evenly distributed recesses 5 and the uniform slow cooling is executed. The uniform initial solidified shell is formed in the molten steel cast in the mold and the vertically short steel ingot having no surface cracks and other defects is formed at a good yield.