A desulfurization apparatus comprising: a blowdown water line (L 1) for introducing boiler cooling tower blowdown water discharged from a cooling tower for a boiler; an organic matter remover disposed on the blowdown water line (L 1) to remove organic matter in the boiler cooling tower blowdown water by activated carbon; an absorber configured to absorb sulfur oxides in flue gas from the boiler; and a makeup water introducing line (L 20) for introducing the boiler cooling tower blowdown water from which the organic matter has been removed as makeup water for the absorber, wherein a plurality of the organic matter removers (21-1 to 21-5) are connected in series on the blowdown water line (L 1), and each of the organic matter removers (21-1 to 21-5) includes an organic matter adsorption filter (22-1 to 22-5) disposed on the blowdown water line (L 1) to remove organic matter in the boiler cooling tower blowdown water, wherein the organic matter adsorption filter (22-1 to 22-5) is an activated carbon filter; a main channel opening/closing valve (V 1 to V 5) disposed on an inlet side of the organic matter adsorption filter (22-1 to 22-5) to open and close inflow of the boiler cooling tower blowdown water; a bypass line (L 11 to L 15) branching from the blowdown water line (L 1) on an upstream side of the main channel opening/closing valve (V 1 to V 5) and bypassing the organic matter adsorption filter (22-1 to 22-5) to connect to the blowdown water line (L 1) on an outlet side of the organic matter adsorption filter (22-1 to 22-5); and a bypass opening/closing valve (V 11 to V 15) disposed on the bypass line (L 11 to L 15) to open and close inflow of the bypassed boiler cooling tower blowdown water. a blowdown water line (L 1) for introducing boiler cooling tower blowdown water discharged from a cooling tower for a boiler; an organic matter remover disposed on the blowdown water line (L 1) to remove organic matter in the boiler cooling tower blowdown water by activated carbon; an absorber configured to absorb sulfur oxides in flue gas from the boiler; and a makeup water introducing line (L 20) for introducing the boiler cooling tower blowdown water from which the organic matter has been removed as makeup water for the absorber, wherein a plurality of the organic matter removers (21-1 to 21-5) are connected in series on the blowdown water line (L 1), and each of the organic matter removers (21-1 to 21-5) includes an organic matter adsorption filter (22-1 to 22-5) disposed on the blowdown water line (L 1) to remove organic matter in the boiler cooling tower blowdown water, wherein the organic matter adsorption filter (22-1 to 22-5) is an activated carbon filter; a main channel opening/closing valve (V 1 to V 5) disposed on an inlet side of the organic matter adsorption filter (22-1 to 22-5) to open and close inflow of the boiler cooling tower blowdown water; a bypass line (L 11 to L 15) branching from the blowdown water line (L 1) on an upstream side of the main channel opening/closing valve (V 1 to V 5) and bypassing the organic matter adsorption filter (22-1 to 22-5) to connect to the blowdown water line (L 1) on an outlet side of the organic matter adsorption filter (22-1 to 22-5); and a bypass opening/closing valve (V 11 to V 15) disposed on the bypass line (L 11 to L 15) to open and close inflow of the bypassed boiler cooling tower blowdown water. an organic matter adsorption filter (22-1 to 22-5) disposed on the blowdown water line (L 1) to remove organic matter in the boiler cooling tower blowdown water, wherein the organic matter adsorption filter (22-1 to 22-5) is an activated carbon filter; a main channel opening/closing valve (V 1 to V 5) disposed on an inlet side of the organic matter adsorption filter (22-1 to 22-5) to open and close inflow of the boiler cooling tower blowdown water; a bypass line (L 11 to L 15) branching from the blowdown water line (L 1) on an upstream side of the main channel opening/closing valve (V 1 to V 5) and bypassing the organic matter adsorption filter (22-1 to 22-5) to connect to the blowdown water line (L 1) on an outlet side of the organic matter adsorption filter (22-1 to 22-5); and a bypass opening/closing valve (V 11 to V 15) disposed on the bypass line (L 11 to L 15) to open and close inflow of the bypassed boiler cooling tower blowdown water.