a wet scrubber (110) which reacts exhaust gas generated from an exhaust gas generator included in a vessel with a reaction solution to convert carbon dioxide included in exhaust gas into ammonium salt;

an inlet (115) which makes inflow of exhaust gas into the inside of the wet scrubber (110) and an outlet (112) which discharges exhaust gas to the outside of the wet scrubber (110);

a circulation tank (120) which produces a reaction solution reacted with exhaust gas and supplies the produced reaction solution to the wet scrubber (110), a transfer pump (123) which transfers ammonium salt produced by reacting carbon dioxide included in exhaust gas flowed through the inlet (115) with the reaction solution, a mixing tank (130) which includes an impeller (135) that produces slurry including carbonate and an ammonia solution by reacting ammonium salt transferred from the wet scrubber (110) with bivalent metal oxide or bivalent metal hydroxide, the sludge pump (131) which transfers sludge from the mixing tank (130) to a solid-liquid separator (150), a solid-liquid separator (150) which separates precipitate such as carbonate and an ammonia solution from the sludge transferred from the mixing tank (130);

a first storage tank (151) which stores an ammonia solution separated from the solid-liquid separator (150);

a second storage tank (160) which stores precipitate such as carbonate separated from the solid-liquid separator (150);

a third storage tank (140) which supplies bivalent metal oxide or bivalent metal hydroxide; and

a transfer pump (152) which transfers an ammonia solution stored in the first storage tank (151) to the circulation tank (120).