To provide a technology which is unnecessary for providing any introduction passage or exhaust passage of compressed air in a casting die, unnecessary for storing a casting taken out of the casting die in a heating furnace, and high in capacity for removing a sand core.

In order to remove a sand core 18 out of a casting 16 with the sand core 18 cast therein, air heated at the temperature (for example, 400°C) at which the shape-holding force of a shape-holding resin of the sand core 18 is degraded is blown into an opening of the casting 16 consisting of one ends 18a-18f of the sand core 18, and sand and gas are sucked from an opening consisting of the other ends 18g-18i of the sand core 18 to give a blow to the casting 16. A compound event consisting of an event that high-temperature air entering the sand core heats the sand core 18 to degrade the shape-holding force of the shape-holding resin, an event that sand grains are blown with high-pressure air, and an event that a crack is generated in the sand core by the blow, and the sand core which cannot be removed by a conventional technology can be removed thereby.