PURPOSE: To make cooling rate faster, fine crystals and form the surface layer of high strength by depositing the water-containable porous material composed of heat- resistant material on the entire surface of the outside wall surface of a metal mold.

CONSTITUTION: Water-containable porous material 2 composed of heat-resistant material is deposited on the outside wall surface of a metl mold 1. The water-containable porous material 2 may be readily deposited by spraying the heat-resistant material having continuous cells with a spray or the like on the outside wall surface of the metal mold 1. If a suitable amount of water is beforehand impregnated in the porous material 2 at the casting, the moisture impregnated in the porous material 2 evaporates when the heat of the casting transfers to the outside wall surface of the metal mold 1. The temperature of the metal mold 1 is abruptly lowered by the evaporation heat thereof, whereby the solidification of the casting is completed earlier. At the time when the cast body solidifies completely, the water content having been impregnated has completely evaporated and thereafter the porous material 2 shuts off the outside air and therefore heat-retaining effect improves, internal stress is removed and cracking is prevented.