PURPOSE: To permit the correct control of a pouring amount by a method wherein the amount of harmful micro constituents in exhaust gas is estimated from the amount of harmful micro constituents in fuel, a reference amount of harmful constituents, which is obtained from the amount of exhaust gas, and the air excessive rate and the like of a fluidized bed combustion device, in a device, in which the amount of harmful micro constituents is controlled by pouring a treating agent into the exhaust gas.

CONSTITUTION: The amount of harmful micro constituents in exhaust gas discharged from a fluidized bed combustion device 7 into an high-temperature pipeline for exhaust gas is operated in an operating means 25 from an air excessive rate, the staying time of gas in a fluidized bed 10 and a reference amount of harmful micro constituents. In this case, the air excessive rate is obtained from a solid hydrocarbon fuel supplying amount and an air supplying amount, the staying time of gas in the fluidized bed 10 is obtained from the height of the fluidized bed and the reference amount of harmful micro constituents is obtained from the supplying amount of solid hydrocarbon fuel, a previously analyzed contents of harmful micro constituents and the amount of exhaust gas of combustion. The optimum amount of treating agent against the obtained amount of harmful micro constituents is injected from a treating agent pouring nozzle 1 to reduce the amount of harmful micro constituents discharged out of a chimney.