A method is disclosed that monitors and controls the condition of an expandable mixture before injecting it in a mold and that maintains the conditions for filling so as to make a casting mold having a uniform strength. The method comprises (a) a step of measuring the temperature of the expandable mixture, (b) a step of determining each reference value of the one or more characteristic parameters that show a characteristic property of the expandable mixture based on the measured temperature and the predetermined relationship between a characteristic property of an expandable mixture and its temperature, (c) a step of measuring the one or more characteristic parameters that show the condition of the mixing of the expandable mixture, (d) a step of determining whether each characteristic parameter is within the corresponding reference value, and (e) a step of determining whether the expandable mixture has been made under the normal condition or if it needs to be adjusted.