PURPOSE: To effectively use an unreacted desulfurizing agent, to achieve high desulfurization efficiency with a simple system by spraying water, while fluidized-mixing the particles incorporating unreacted desulfurizing agent recovered after the desulfurization reaction, and supplying the unreacted desulfurization agent again into the desulfurization tower.

CONSTITUTION: The desulfurizing agent A sprayed into the desulfurization tower is reacted with acidic toxic gas such as SO2 in the exhaust gas, and the reacted desulfurizing agent A is collected by the dust collector 5 with an ash in the exhaust gas and the unreacted desulfurizing agent. Unreacted and reacted desulfurizing agent A and residual particles incorporating ash exhausted from dust collector 5 is fluidized and mixed by air C or exhaust gas D in the regeneration device 6 and moisturized by the sprayed water B from a nozzle 7. Further, by heating the particles in the heating section 8, water B present between the particles of the desulfurization agent A is removed and the flocculation of the desulfurizing agent A is diminished. Such treated desulfurization agent A is supplied while spraying it again into the duct 4 or the desulfurization tower and is reacted with the acidic toxic gas in the exhaust gas such as SO2.