PURPOSE: To control reduction ratio and production speed for reduction of ores, by detecting reducing reaction loading distribution ratio at each step from gas component, reduction ratio of ores, etc., charged and discharged in each step and controlling grain residence quantity in each step based on the detected values.

CONSTITUTION: Preheated ore 2 is supplied to a first step reduction furnace 5 and reducing gas 7 is supplied to a second step reduction furnace 6. A large part of ores is circulated through a pneumatic valve 11a and a part of ore is fed to the second reduction furnace 6 and circulated through a pneumatic valve 11b by blowing new reducing gas 13 and a part is taken out as product 14. Then, the reducing gas component is analyzed by gas analyzers 20a, 20b, 20c, to input in a process computer 30 and the reduction ratio is assumed by ore samplers 21a, 21b, to input in the computer 30. When the difference between the aimed gas oxidizing degree and the actual gas oxidizing degree is become to ≥3%, the computer 30 operates the reduction loading and variety of ore circulating quantity in the valve 11a, 11b is commanded, to change the grain residence quantity in the fluid reduction furnaces 5, 6.