An exhaust gas treatment apparatus comprising: a reaction tower which has two or more openings with different areas through which an exhaust gas is introduced, and two or more exhaust gas introducing pipes which are provided corresponding to the two or more openings with different areas and carry the exhaust gas and which have valves which select whether to introduce the exhaust gas into the reaction tower or not, wherein the exhaust gas introducing pipes are connected to the two or more openings so that the introduced exhaust gas swirls inside the reaction tower, the two or more openings are provided respectively at different positions in a height direction which is a direction from a bottom side where the exhaust gas is introduced to a top side where the exhaust gas is emitted in the reaction tower, an opening area of an opening which is arranged on the bottom side of the reaction tower is larger than an opening area of an opening which is arranged on the top side of the reaction tower, the reaction tower has a cylindrical shape which extends in the height direction, a horizontal cross section which is perpendicular to the height direction of the reaction tower is a circular shape, and the two or more exhaust gas introducing pipes connect in the tangential direction of the horizontal cross section which is a circular shape, wherein in the two or more openings, a total opening area which contributes to introducing the exhaust gas into the reaction tower is variable, and wherein the exhaust gas treatment apparatus further comprises an opening controlling unit which controls the opening area depending on a flow rate of the exhaust gas which is introduced into the reaction tower by controlling the valves, the exhaust gas treatment apparatus further comprises a flow controlling unit which controls a supply amount of a liquid which is supplied to an inner part of the reaction tower for treating the exhaust gas depending on the total opening area which contributes to introducing the exhaust gas into the reaction tower. a reaction tower which has two or more openings with different areas through which an exhaust gas is introduced, and two or more exhaust gas introducing pipes which are provided corresponding to the two or more openings with different areas and carry the exhaust gas and which have valves which select whether to introduce the exhaust gas into the reaction tower or not, wherein the exhaust gas introducing pipes are connected to the two or more openings so that the introduced exhaust gas swirls inside the reaction tower, the two or more openings are provided respectively at different positions in a height direction which is a direction from a bottom side where the exhaust gas is introduced to a top side where the exhaust gas is emitted in the reaction tower, an opening area of an opening which is arranged on the bottom side of the reaction tower is larger than an opening area of an opening which is arranged on the top side of the reaction tower, the reaction tower has a cylindrical shape which extends in the height direction, a horizontal cross section which is perpendicular to the height direction of the reaction tower is a circular shape, and the two or more exhaust gas introducing pipes connect in the tangential direction of the horizontal cross section which is a circular shape, wherein in the two or more openings, a total opening area which contributes to introducing the exhaust gas into the reaction tower is variable, and wherein the exhaust gas treatment apparatus further comprises an opening controlling unit which controls the opening area depending on a flow rate of the exhaust gas which is introduced into the reaction tower by controlling the valves, the exhaust gas treatment apparatus further comprises a flow controlling unit which controls a supply amount of a liquid which is supplied to an inner part of the reaction tower for treating the exhaust gas depending on the total opening area which contributes to introducing the exhaust gas into the reaction tower.