Abstract: A fluidized bed reactor for the pyrolysis of pieces of rubber or the like, especially old tires the reactor comprising a container at the lower part of which there is discharge device for non-volatile pyrolysis products; gas blowing nozzles arranged in a zone above the discharge device for supplying a fluidizing gas and for producing a fluidized bed from material such as sand or alumina added to the reactor; preferably a heating device, especially one comprising heating tubes extending across the container; a gas outlet disposed in the zone above the fluidized bed; and supply means for conveying pieces of material to be pyrolized to the container; this apparatus is characterized by the fact that the gas blowing nozzles are arranged to direct the gas downwardly, that at least one group of nozzles are arranged in a common horizontal plane, and that the material supply device is such that its dimensions are comparable with the cross-sectional surface of the fluidized bed.