A method of suppressing slag foaming that can grasp a state of slag foaming in the continuous melting furnace and accurately suppress the slag foaming so as to enable continuous production of molten metal in a stable state. This method includes charging of a suppressor into slag in the furnace, measuring a flow rate of a flue gas discharged from the continuous melting furnace during blowing of the slag over time, increasing a charging speed rate of the suppressor if the flue gas flow rate has an increasing tendency and decreasing the charging speed rate of the suppressor if the flue gas flow rate has a decreasing tendency.