Treatment of molten iron

A method for treating molten cast iron includes, performing an inoculation treatment to the molten cast iron, with the use of an inoculant containing : 15 to 80 wt % Si; either 80 to 100 wt % purity La or 80 to 100 wt % purity Ce as RE; Ca; Al; and the balance Fe with inevitable impurities, by adding the inoculant to the molten cast iron such that : the addition amount of La or Ce relative to the molten cast iron is 0.001 to 0.009 wt %; the addition amount of Ca relative to the molten cast iron is 0.001 to 0.02 wt %; and the addition amount of Al relative to the molten cast iron is 0.001 to 0.02 wt %.