[en] A crucible for melting radioactive wastes has a double-walled structure comprising an outer cylinder, a crucible main body contained therein and powders filled therebetween. The outer cylinder is made of a heat-resistant high-alumina, mullite or magnesia refractories. Aggregates such as SiC or Al₂O₃ sintered with an electroconductive carbon bond so as to generate Joule heat by high frequency induction are used for the crucible main body. Then, heat-resistant materials such as of corundum or magnesia spinels are used as the powders. Accordingly, even if the crucible should be broken, the molten materials are certainly prevented from flowing to the outside by the outer cylinder. (I.N.)