Abstract: An apparatus for fixing radioactive or toxic waste has an extruder including a mixing mechanism for intermingling and advancing the waste and a carrier material introduced into the extruder. The extruder has a heating zone with which there communicates a vapor outlet device having an observation window. Within the vapor outlet device there is disposed an arrangement for cleaning the window and an arrangement for removing deposits from those locations of the vapor outlet device that are adjacent the mixing mechanism. The condenser is coupled to a distillate accumulator with the interposition of two alternatingly operating filters for removing particles from the condensate obtained from the condenser. To the outlet of the extruder there is coupled a loading device in which containers are successively filled with the material discharged by the extruder.