PURPOSE: To provide a denitration method capable of reducing necessary fuel cost, by oxidizing CO contained in the waste gas of a sintering furnace raised in temp., and denitrating it with an iron ore catalyst and gaseous ammonia.

CONSTITUTION: The waste gas to be denitrated is raised in temp. to about 270°C with a heat exchanger, and introduced into a CO oxidizing apparatus 10 packed with a CO oxidizing catalyst to heat it to 350°C or above, by this oxydation. After that like the conventional method, ammonia 7 is added and immediately introduced to the denitration reactor 8, where nitrogen oxides in the waste gas are reduced with said catalyst and converted into harmless N2. It is cooled with the heat exchanger 4 to about 130°C and discharged from a stack 9. In that case, a reheating furnace 6 is used for starting up the denitration device 8 until it becomes a stationary state, or for backing it up when the CO concn. lowers.