To include a boiler 11 that burns fuel F, an air heater 13 that recovers heat of flue gas 18 from the boiler 11, a first precipitator 14 that reduces dust in the flue gas 18 after heat recovery, a desulfurizer 15 that reduces sulfur oxides in the flue gas 18 after dust reduction by an absorbent, a dewaterer 32 that reduces gypsum 31 from desulfurization discharged water 30 discharged from the desulfurizer 15, a spray drying device 34 including an atomizer that atomizes a dewatering filtration fluid 33 discharged from the dewaterer 32, and a flue-gas introducing line L11 that introduces a part of the flue gas 18 into the spray drying device 34.