A device for the fluidized bed cracking of a hydrocarbon charge using two reaction chambers linked together by a cooling particles transferrer, a fractionating column and conduits to supply the hydrocarbonated effluents from each of the two chambers to the fractionating column. The fractionating column has, internally, at least two different areas: a first partitioned fractionating area in the form of two compartments, each of which communicates with a second common fractionating area. The conduits for the supply of effluents from the first and the second reaction chamber terminate, respectively, in the first and second compartment of the partitioned fractionating area. A recycler and an injector are provided for recycling and injecting into one of the reaction chambers of at least one cut drawn off from the partitioned fractionating compartment of the effluents of the other reaction chamber.