A solidification processing apparatus for radioactive waste materials comprises a tank for a solidifying agent for solidifying the radioactive waste materials, a waste material vessel connected to the tank for the radioactive waste materials, a pouring control unit for controlling pouring of the solidifying agent into the vessel, and a heating and curing chamber for heating the vessel by an indirect heating unit after pouring the solidifying agent onto the waste materials in the vessel to polymerize and set the solidifying agent, thereby solidifying the radioactive waste materials. With this arrangement, the solidifying agent superior in impregnation is poured into a vessel filled with radioactive waste materials, whose poured amount is controlled by the pouring control unit. After pouring the solidifying agent into the vessel, the vessel is heated indirectly by an indirect heating unit in order to avoid deflagration if the solidifying agent is combustible. The solidifying agent is polymerized and set in a relatively short time by promoting the polymerization reaction of the agent to solidify the radioactive waste materials with stability.