A process is disclosed for discharging and transferring upwardly fluidized particles from a dense fluidizing layer forming section to a high-velocity transferring section having a diameter which is smaller than that of the dense fluidizing fluidized layer forming section, wherein at least one intermediate cylindrical section is provided between the dense fluidizing fluidized layer forming section and the high-velocity transferring section. The process can decrease the degree of changes in the amount of particles to be discharged from the dense fluidizing layer forming section and transferred by the riser, thereby proving a stable and uniform transfer of the fluidized particles.