To provide an apparatus which lowers the temperature of an removes a harmful gas (fly ash, dioxins, HCl, and SOx) from a combustion gas while supplying chemicals by installing a cooling water spray nozzle, a recirculation dust collection section, and a recirculation gas nozzle in a centrifugal dust collector.

This apparatus is equipped with a cooing water spray nozzle 4 set up in an inner pipe 3, a recirculation dust collection section 2, a recirculation gas nozzle 8 set up on the outer surface of the inner pipe 3, and adjustment sections (for the amounts of cooling water and a recalculated gas, at the upper and lower positions of the nozzle 4).