PURPOSE: To manufacture an inexpensive foaming inhibitor having an immediate effect by adding a surfactant and a binder to starting materials contg. oil and including dust, sludge, mill scale, fine ore or fine sintered ore, kneading them, molding the mixture, and solidifying it by drying.

CONSTITUTION: A prescribed amount of a surfactant and a prescribed amount of a binder such as Portland cement or quick lime are added to starting materials contg. oil and including one or more among dust, sludge, mill scale, fine ore and fine sintered ore. The amount of the surfactant added depends on the oil content, and water may be added. They are kneaded with a kneader such as a mixer, and the mixture is molded to about 50W100mm size with a molding machine. The resulting molded raw foaming inhibitor is solidified by drying. Thus, a foaming inhibitor having an immediate effect is manufactured by utilizing inexpensive starting materials. The inhibitor is very effective in inhibiting the foaming phenomenon of slag at once.