PURPOSE: To insert safely and deeply the titled inserter into molten metal by heat treating a rodlike body made of cellulose-base substance to regulate the residual volatile substance to an amount suitable for bubbling.

CONSTITUTION: Molten cast iron 2 is received in an extra-small-sized ladle 1, covered with a layer 3 of a previously charged desulfurizing agent, and kept at the temp. A rodlike body made of cellulose-base substance is heat treated to remove a volatile substance which is separated in large quantities at a relatively low temp., thereby regulating the residual volatile substance to an amount most suitable for bubbling. The resulting inserter 5 for bubbling is attached to a portable grasping and inserting tool 4 and inserted into said molten metal 2. The inserter 5 generates a gas deep in the molten metal 2, agitates the molten metal 2, and brings it into contact with the layer 3 to allow the desulfurization reaction to proceed. By suitably moving the tool 4 as required, the desulfurization is accelerated.