To provide an apparatus and method for rigidly solidifying radioactive waste, which does not require cleaning equipment and cleaning processes.

A radioactive waste solidification apparatus includes an airtight vessel 1 with an openable/closable inlet port 11A through which radioactive waste is poured in, and agitation means 2 for agitating and mixing radioactive waste poured into the airtight vessel 1 with a solidification material preloaded therein after closing the inlet port 11A to hermetically seal the airtight vessel 1. The radioactive waste solidification apparatus agitates and mixes radioactive waste with the solidification material preloaded in the airtight vessel 1 and allows the mix to solidify in the hermetically sealed airtight vessel 1 into which the radioactive waste was poured. Thus, the apparatus does not use a mixer drum as in the out-drum mixing method and does not require attaching and detaching of an agitation blade to and from the vessel as in the in-drum mixing method, which eliminates the need for cleaning equipment and cleaning process for cleaning the mixer drum and agitation blade. Furthermore, agitating and mixing radioactive waste with the solidification material results in rigidly hard solidified radioactive waste.