To solve a problem that a large scale facility is required because an 'opening machine' and a 'mud gun' are conventionally employed for opening/closing the delivery gate of a furnace and the work is troublesome because they are used alternately and a choking material, i.e., 'mud', must be supplied, and to simplify the facility and the work while eliminating the material.

A current is induced in a sleeve 7 made of conductive refractories by conducting a coil 8 at the delivery gate of a furnace and a choking ore is heated by its conduction heat and melted thus starting delivery of molten. At the time of ending delivery of molten, power supply is stopped and the ore in the sleeve 7 is cooled by radiating heat and solidified thus choking the delivery gate.