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.

An almost cylindrical-shaped sliding bearing which is the cast iron part, is composed of a flaky graphite cast iron part and a foaming cast iron part. A cylindrical foaming promoter 23 for promoting the foaming at the solidifying time of molten cast iron having hyper-eutectic composition, is beforehand disposed in a cavity 25 in a sand mold 17 relevant to the foaming cast iron part, and the molten cast iron having the hyper-eutectic composition is poured into the cavity 25 from a spouting hole line 2 in a core 18. In this case, a portion where the molten cast iron is mixed while being in contact with the foaming promoter 23, becomes the foaming cast iron part by promoting the foaming at the solidifying time of the molten cast iron, and a portion where the molten cast iron is not in contact with the foaming promoter 23, becomes the flaky graphite cast iron part at the solidifying time. The flaky graphite cast iron part at the inner peripheral side of the sliding bearing has excellent wear resistance and the foaming cast iron part at the outer peripheral side of the sliding bearing has more excellent damping capacity than that at the flaky graphite cast iron part.