The 2-stage fluidized bed furnace for pre-reducing a fine iron ore comprises a first stage fluidized bed furnace for receiving the fine iron ore from a storage hopper, discharging medium/small particle size iron ore to the upper part thereof, and reducing a coarse particle size iron ore while forming a bubbling fluidized bed; a second stage fluidized bed furnace for receiving the medium/small particle size iron ore discharged from the upper part of the first stage and reducing it while forming a turbulent fluidized bed; and a first hot cyclone for collecting the small particle size iron ore contained in the discharged gas from the second stage fluidized bed furnace, the first stage furnace being formed in an upper-narrowed, lower-expanded shape and comprising a narrow, upper portion, a transitional, slanted portion and a wide, lower portion, the second stage furnace being in an upper-expanded, lower-narrowed shape and comprising a wide, upper portion, a transitional, slanted portion and a narrow, lower portion.