To prepare high-strength high-reactivity coke for blast furnaces without detriment to chamber type coke oven side walls.

In this method, 0.05-5 mass % of iron is added to coal, and carbonization proceeds with the coke oven wall temperature kept at 1,100°C or lower. Iron ore or iron dust should be the iron source. It is desired that the coke oven combustion chamber bottom temperature be adjusted so that the coke oven wall surface temperature stay below 1,100°C throughout the entire carbonization period from just after coal injection through just before coke extraction.