To prevent such an accident that a combustion gas from a main tuyere is blown out to the outside of a furnace.

In the operating method for this gasification melting furnace, a gasified object and cokes are thrown in the gasification melting furnace, the combustion gas is blown from the tuyere formed in a furnace side wall into the furnace to partially burn the gasified object. Thus, an inflammable gas is generated, and residues are molted at a hearth part and discharged to the outside of the furnace. The molten slag discharged to the outside of the furnace is thrown in the gasification melting furnace to maintain the amount of the molten slag accumulated in the hearth part at a specified amount.