To improve combustion capability of coal having low ignitability such as highly carbonized anthracite, and also to reduce the concentration of nitrogen oxide (NOx) in combustion waste gas.

By supplying an oxygen-containing organic compound to airflow conveying powdered coal, for example a hydroperoxy radical (HOO-) is produced by the decomposition of the oxygen-containing organic compound, and by oxidizing a condensation aromatic compound with the hydroperoxy radical, combustion capability of the powdered coal is accelerated, and combustion characteristics are enhanced. The hydroperoxy radical oxidizes NO produced by combustion to NO2, the NO2 is decomposed to nitrogen with unburned hydrocarbon, and the amount of nitrogen oxide (NOx) in the combustion waste gas is reduced.