PURPOSE: To easily process a cast product by applying annealing under the specific condition after casting to part for executing the processing of the cast product, which is cast by using a metallic mold, and softening.

CONSTITUTION: By pouring molten iron composed of cast iron component corresponding to JIS FC20-FC30 into the metallic mold, a cam shaft 1 is cast, and at the time, when the molten iron surface layer part 1a in contact with the metallic mold becomes shell-state solidified layer having high hardness chilled structure, the casting is released from the metallic mold. Under red condition (about 600-900°C) of the cam shaft 1 released from the metallic mold, a journal part 1 as the softening necessary part is rapidly heated to 1000-1100°C with a high frequency heating member 4. At this time, the temp. of part except the journal part 3 is the temp. of A1 transformation point or lower. Under this condition, the annealing for relieving casting stress is executed to the cam shaft 1 by using an electric furnace under condition of 550-600°C×2H and natural cooling is executed. By this method, only the journal part 3 can be softened.