A method includes measuring a water content and a magnetized matter content of molding sand discharged from green sand casting equipment; comparing the measured water content with a first control value, and if the water content exceeds the first control value, drying the molding sand until the water content becomes equal to or less than the first control value; comparing the measured magnetized matter content with a second control value, and if the magnetized matter content exceeds the second control value, magnetically separating the molding sand until the magnetized matter content becomes equal to or less than the second control value; thereafter, reclaiming the molding sand by dry mechanical reclamation until a loss-on-ignition becomes equal to or less than a third control value; and classifying the molding sand until a total clay content becomes equal to or less than a fourth control value.