To provide a cast iron part and its producing method with which an application range of the cast iron parts can be made to wide.

A chuck for lathing which is the cast iron part, is composed of a spheroidal graphite cast iron part and a foaming cast iron part. Molten foaming cast iron is poured into a cavity 17 from a sprue 14 through a first runner 15 and a second runner 16, and the lower part side in the cavity 17 is filled up with the molten cast iron from the first runner 15 and the upper part side in the cavity 17 is filled up with the molten cast iron subjected to spheroidizing treatment in a reaction chamber 16a in the second runner 16 to perform a molten cast iron pouring process. The foaming cast iron part, with which the molten cast iron to be contained on the lower part side in the cavity 17 and subjected to the foaming treatment is foamed at the solidifying time, and the spheroidal graphite cast iron with which the graphite in the molten cast iron to be contained on the upper part side in the cavity 17 is spheroidized at the solidifying time by applying the spheroidizing treatment, are integrally formed by solidifying the molten cast iron through the molten cast iron pouring process into the cavity 17.