A method and device are provided for direct reduction of ore fines in a wide range of particle size, the reducing agent being hydrogen placed in a fluidized bed gutter with a plurality of sequentially arranged chambers. The fluidization rate in the supply base is set so that a defined class of particle size remains in the chamber concerned where it will be submitted to a reduction process and that the finest particle size fraction is discharged from the chamber, then precipitated in a hot gas cyclone to solid material (or fines) and gas. The ore fines precipitated in the cyclone then reaches the following chamber. The gas from all the hot gas cyclones is fed by a collector to the pre-heater. After reduction in the chambers, the ore fines are conveyed in pressure vessels for submission to further processes.