To provide a method for manufacturing a cast iron shaft which can manufacture the cast iron shaft as a one-piece product containing a variety of metallographic structures and being excellent in abrasion resistance by controlling cooling and so on in a mold.

After molten metal is poured into a cavity 7, the surface of the product is solidified to an extent that the product does not get out of shape in the cavity, by the removal of heat via the mold bodies 1 and 2 and eight sets of movable insert dies 3A-5B. Then seven sets of the insert dies 4A, 4B, 5A and 5B are quickly separated from the solidified surface of the product. The insert dies and the facing portions of the product surface are kept in a non-contact state for approximately 20 seconds. Further four sets of the insert dies 4A and 4B out of the separated insert dies are made to contact the surface of the product again, and the re-contact state is kept for approximately 30 seconds. Then the product is taken out of the insert dies. Mainly a martensitic structure is formed at the portions of the product facing the four sets of the insert dies 4A and 4B which repeat separation and contact.