Provided is a method of producing foamed sand (s) for forming a sand mold. The foamed sand (s) includes sand particles (p) and foam (f) adhering to surfaces of the sand particles (p). The foam (f) contains water glass (b), water (w), and a surfactant (c). According to the method, an aqueous surfactant solution (e) in which the surfactant (c) is dissolved is frothed to generate froth (d) from the aqueous surfactant solution (e). Then, the generated froth (d), the water glass (b), and the water (w) are kneaded with the sand constituted by the sand particles (p).