PURPOSE: To provide a harmless briquet which converts harmful carbon monoxide produced during combustion into harmless carbon dioxide by oxidation, prepared by kneading a main fuel component such as coal powder and char powder, a granulation binder and a metal oxide (hydroxide) which contains water of crystallization.

CONSTITUTION: A main fuel component consisting of coal powder, coke powder, charcoal powder or a mixture thereof, a granulation binder consisting of clay, cellulose, red aglae, starch paste or tar pitch and a crystallization water-containing metal oxide or metal hydroxide which undergoes thermal decomposition at a relatively low temperature and releases water of crystallization, or a mixture thereof (e.g. dried aluminum hydroxide sludge) are mixed by kneading and the mixture is formed into briquet. When burned, the briquet releases water vapor which reacts with harmful carbon monoxide to convert it into harmless carbon dioxide as shown by the reaction formula.