To provide a method and an apparatus for casting a piston for internal combustion engine with which a sound internal quality is obtained by restraining the development of shrinkage hole at the thick part of a product, and since a close surface layer is formed on the top surface of the piston in the product, the surface layer part has the close solidified structure and the mechanical strength is improved.

The portion corresponding to the top surface of the piston in a cavity for product forming part is formed as a separated insert die 3, and in the insert die 3, an internal cooling circuit 4 is arranged and cooling medium is supplied into this internal cooling circuit 4, and molten metal filled up in the above cavity is rapidly cooled with the insert die 3 by cooling the portion corresponding to the top surface 10 of the piston in the above cavity for product forming part. Further, pins 2 are inserted into opening parts opened in boss parts 9, 9' in the cavity except the product forming part connected to the thick parts 11, 11' in the above cavity for product forming part through a communicating part, and after starting the solidification of the molten metal filled up, the above pins 2 are pushed in to locally pressurize the above boss parts 9, 9'.