PURPOSE: To simplify the constitution of a fluidized bed furnace for executing pre-reduction in a smelting reduction device for ore and to improve the average pre-reduction ratio of the whole ore.
CONSTITUTION: A small diameter cylindrical part 22 and a large diameter cylindrical part 24 at the upper part thereof through a hollow reverce truncated conical part 23 are formed. Reduction gas is supplied in a wind box 26 at the lower part than a dispersion plate 25 in the small diameter cylindrical part 22 and the fluidized bed of coarse grain is formed in the small diameter cylindrical part, and the coarse grain is discharged from a coarse grain discharging hole 28 near the dispersion plate. In the large diameter cylindrical part 24, small grain is fluidized and discharged by overflowing from a small grain discharging hole 30. The small grain or fine powder scattered from the large diameter cylindrical part 24 are made to be extremely few and a cyclone 41 is made to be miniaturized and can be placed to the low position so as not to circulate the fine powder.