Abstract: Provided is a cast-iron product that satisfies demands for both weight reduction and strength enhancement with good balance. A cast-ion product having an inner honeycomb structure is produced by a process including: a decarburization step, in which a cast-iron product made of a hypoeutectic cast iron is heated to form a decarburized layer on the surface of the cast-iron product; an outflow-hole formation step, in which an outflow hole penetrating through the decarburized layer into an inner region is formed; and a liquation step, in which the cast-iron product is heated to a temperature lower than the melting point of the decarburized layer and higher than the melting point of the hypoeutectic cast iron remaining inside, while being held in such a manner that the outflow hole is located in the lower portion thereof.