An object material to be melted (radioactive liquid waste and glass material) 16 is charged into the interior of a cold-crucible induction melting apparatus 10, and a conductor 18 the melting point of which is higher than that of the glass material is inserted into a melting furnace 12. A high-frequency current is supplied to a coil 14 so as to generate heat in the conductor and indirectly heat the glass material. The conductor is withdrawn after a part of the glass material has been put in a molten state. The glass material as a whole is thereafter kept in a molten state while maintaining the induction heating by the molten glass material. The conductor inserted into the melting furnace is, for example, a silicon carbide rod. The surface of the molten material which contacts the inner surface of the melting furnace turns into a solid layer (skull) due to cooling, so that the molten material does not directly contact the refractories. This enables the high-temperature corrosion of the melting furnace to be prevented.