By mixing, stirring and kneading, with water glass (11) as a binder, sand (7), a surfactant (9), and water (10), foamed sand (S) is generated. The foamed sand (S) is packed in a cavity of a metallic mold and solidified to form a sand mold. By using the sand mold, aluminum is cast. By using water glass that is an inorganic binder, during casting, harmful gas and odor are not generated. Further, when a molar ratio n of water glass (Na20 nSiO2 mH2O) is adjusted in the range of 0.65 to 1.30, a quantity of water (H2O) generated by heating water glass with a high temperature melt during casting can be suppressed. Thereby, hydrogen gas (H2) according to a reaction between water (H2O) and aluminum (Al) can be suppressed from being generated and casting quality can be improved.