A powder discharge system having a circulating water tank for collecting powder generated when an exhaust gas is treated in an exhaust gas treatment apparatus, the powder discharge system comprising: at least one eductor provided in the circulating water tank; the eductor comprising a nozzle configured to throttle a flow of water supplied from a pump for pumping water in the circulating water tank, a suction port configured to suck water in the circulating water tank into the eductor by utilizing a reduction of pressure generated when the flow of water is throttled by the nozzle, and a discharge port (3 OUT) configured to eject the water sucked from the suction port together with the water discharged from the nozzle toward a bottom of the circulating water tank to crush powder deposited on the bottom of the circulating water tank and to float the powder; and a drainage port provided in the circulating water tank to discharge the floating powder through the drainage port from the circulating water tank together with drainage water; wherein the water is ejected from the discharge port (3 OUT) of the eductor; and means for controlling a water level of the circulating water tank to form a state where the water level is lower than the suction port of the eductor and a state where the water level is higher than the suction port of the eductor; wherein, when the water level is lower than the suction port of the eductor, only the water discharged from the nozzle is ejected from the eductor toward the bottom of the circulating water tank; and wherein, when the water level is higher than the suction port of the eductor, the water discharged from the nozzle and the water sucked from the suction port are ejected from the eductor toward the bottom of the circulating water tank. at least one eductor provided in the circulating water tank; the eductor comprising a nozzle configured to throttle a flow of water supplied from a pump for pumping water in the circulating water tank, a suction port configured to suck water in the circulating water tank into the eductor by utilizing a reduction of pressure generated when the flow of water is throttled by the nozzle, and a discharge port (3 OUT) configured to eject the water sucked from the suction port together with the water discharged from the nozzle toward a bottom of the circulating water tank to crush powder deposited on the bottom of the circulating water tank and to float the powder; and a drainage port provided in the circulating water tank to discharge the floating powder through the drainage port from the circulating water tank together with drainage water; wherein the water is ejected from the discharge port (3 OUT) of the eductor; and means for controlling a water level of the circulating water tank to form a state where the water level is lower than the suction port of the eductor and a state where the water level is higher than the suction port of the eductor; wherein, when the water level is lower than the suction port of the eductor, only the water discharged from the nozzle is ejected from the eductor toward the bottom of the circulating water tank; and wherein, when the water level is higher than the suction port of the eductor, the water discharged from the nozzle and the water sucked from the suction port are ejected from the eductor toward the bottom of the circulating water tank.