PURPOSE: To change salt-forming agents to harmless compounds having high heat resistances, by burning fossil fuel, waste, etc., containing moisture at an specific adjusted content at a specific temperature or lower, by adjusting the theoretical ratio between basic materials and the salt-forming agents to a specific value or lower by distributing chlorine-containing materials in the fuel, waste, etc., and adjusting the saturated state of steam.

CONSTITUTION: Fossil fuel, waste, etc., are made to stay in a closed container by adjusting the moisture content of the fuel, waste, etc., to 10-35 wt.% and the theoretical ratio between basic materials and salt-forming agents to 5:1 by distributing basic materials, particularly, calcium carbonate or magnesium carbonated in the fuel, waste, etc. Then, after the saturated state of steam is adjusted, the mixture is burnt on a hearth while the temperature of the hearth is maintained lower than the thermal dissociation temperature of compounds generated from basic materials and halogens. The retention time of the fossil fuel, waste, etc., is the time until they are burned after they are sent to the hearth from a basic material supply station and the temperature of the hearth is adjusted to <850°C. When the fossil fuel, waste, etc., are burned in the above-mentioned way, the purification of the flue gas becomes unnecessary, because the occurrence of acidic gases from the salt-forming agents can be prevented.