PURPOSE: To perform correctly and surely graphite spheroidization of a cast iron by charging a graphite spheroidizing agent into a box delineated in the bottom of a ladle, covering the same with a refractory covering jig, and removing the covering jig upon completion of receiving the molten metal.

CONSTITUTION: A graphite spheroidizing agent A is packed in a box 2 delineated with refractories 3 in the bottom of a ladle 1 and a refractory covering jig 4 is charged into the ladle 1 by means of a crane, etc. and is so installed as to cover the top surface of the agent A by a covering plate 42. A molten metal is then poured into the ladle 1 and when the receiving of the molten metal is completed, the jig 4 is pulled up and removed. The molten metal and the agent A contact with each other through small holes 45 of the plate 42 during the receiving of the molten metal as a result of the above-mentioned operation but the reaction occurring in such reaction is very slight and when the jig 4 is removed upon completion of the receiving of the molten metal, the agent A diffuses from the inside of the box 2 and contacts thoroughly with the molten metal. The spheroidization reaction is thus smoothly and surely effected.