PURPOSE: To reduce the number of working processes and to prevent the development of trouble, such as deformation, crack, by beforehand arranging an exothermic material to the position in a mold corresponding to the position softening a cast product and generating the heat of the exothermic material at the time of cooling after pouring the molten metal into the mold to partially delay the cooling of the cast product.

CONSTITUTION: The molten metal is poured into the mold composed of a sand mold 10 to form a pulley 51, and at the time of cooling the pulley 51 as the cast product, the steel structure at the tip part 51a of a shaft part of the pulley 51 becomes low perlite and high ferrite by generating the heat of the exothermic material M, and then, this part is softening-annealed. Therefore, the cast product can be cooled and solidified in the remained condition in the mold and is unnecessary to take out from a mold. Further, since the take-out of the cast product is made to be unnecessary, the deformation of the cast product is not developed and the loss of the thermal energy is little. Further, since the sand mold 10 is used, the cooling speed is delayed and the chilled structure is not formed on the surface layer part of the cast product.