PURPOSE: To prevent a contamination of molten steel and to obtain a high quality steel ingot by forming a runner by a cast iron casting for a bottom pouring ingot making, which molten steel is supplied into a ingot making mold by the bottom pouring.

CONSTITUTION: A cast iron block 4 for forming runner is a block to form the runner connected with a pouring tube 2 and the ingot making mold 3. Therefore, as the runner, which supplies the molten steel from the pouring tube 2 to the ingot making mold 3, is not formed of refractory, the molten steel is not contaminated caused by erosion of refractory and not afraid of generating any refractory scum, and then the ingot having high quality is obtd.