A casting mold which is molded by heating mulled sand including a mixture of refractory molding sand particles, an inorganic water soluble binder and water, wherein the inorganic water soluble binder is made of a combination of a sulfate compound such as magnesium sulfate heptahydrate and a borate compound such as sodium tetraborate decahydrate. The casting mold is formed by baking the mulled sand in such a manner that at least part of the sulfate compound retains water of crystallization therein and the borate compound is once fused and then cured.