A CO 2 recovery system comprising: an absorption tower that causes CO 2 -containing exhaust gas to come into contact with a CO 2 -absorbing solution and removes CO 2; a regeneration tower that regenerates a rich solution that has absorbed CO 2 by heat exchange; a separation drum that condensates steam released from the regeneration tower in CO 2 gas and separates water, wherein a lean solution produced by removing CO 2 from the rich solution is reused in the absorption tower, a rich-solution supply line that supplies the rich solution to the regeneration tower, and a lean-solution supply line that supplies the lean solution to the absorption tower, wherein the absorption tower includes a CO 2 -recovery unit that causes the CO 2 -containing exhaust gas to come into contact with the CO 2 -absorbing solution and absorbs CO 2 contained in the exhaust gas; at least one washing unit (1013-1, 1013-2) that is arranged in an upper side of the CO 2 -recovery unit, cools CO 2 -removed exhaust gas after CO 2 is removed, and recovers the CO 2 -absorbing solution accompanying the CO 2 -removed exhaust gas; and a condensed-water receiver (1015-1, 1015-2) that is arranged in a lower side of the washing unit (1013-1, 1013-2) and collects condensed water in each washing unit (1013-1, 1013-2); said CO 2 recovery system being characterized in that the absorption tower further comprises a filtration membrane apparatus that filters solid content remaining in the lean solution by using a filter, said filtration membrane apparatus being provided between a lean-solution branch line that supplies the lean solution to be filtered to the filtration membrane apparatus, a cleaning-water supply line that supplies the low-concentration CO 2 -absorbing solution to the lean-solution branch line and a lean-solution branch line that supplies a lean solution without the solid content to the lean-solution supply line, and in that a low-concentration CO 2 -absorbing solution that circulates in the system is used to clean the filter, and the low-concentration CO 2 -absorbing solution used for the cleaning is again returned into the system. an absorption tower that causes CO 2 -containing exhaust gas to come into contact with a CO 2 -absorbing solution and removes CO 2; a regeneration tower that regenerates a rich solution that has absorbed CO 2 by heat exchange; a separation drum that condensates steam released from the regeneration tower in CO 2 gas and separates water, wherein a lean solution produced by removing CO 2 from the rich solution is reused in the absorption tower, a rich-solution supply line that supplies the rich solution to the regeneration tower, and a lean-solution supply line that supplies the lean solution to the absorption tower, wherein the absorption tower includes a CO 2 -recovery unit that causes the CO 2 -containing exhaust gas to come into contact with the CO 2 -absorbing solution and absorbs CO 2 contained in the exhaust gas; at least one washing unit (1013-1, 1013-2) that is arranged in an upper side of the CO 2 -recovery unit, cools CO 2 -removed exhaust gas after CO 2 is removed, and recovers the CO 2 -absorbing solution accompanying the CO 2 -removed exhaust gas; and a condensed-water receiver (1015-1, 1015-2) that is arranged in a lower side of the washing unit (1013-1, 1013-2) and collects condensed water in each washing unit (1013-1, 1013-2); said CO 2 recovery system being characterized in that the absorption tower further comprises a filtration membrane apparatus that filters solid content remaining in the lean solution by using a filter, said filtration membrane apparatus being provided between a lean-solution branch line that supplies the lean solution to be filtered to the filtration membrane apparatus, a cleaning-water supply line that supplies the low-concentration CO 2 -absorbing solution to the lean-solution branch line and a lean-solution branch line that supplies a lean solution without the solid content to the lean-solution supply line, and in that a low-concentration CO 2 -absorbing solution that circulates in the system is used to clean the filter, and the low-concentration CO 2 -absorbing solution used for the cleaning is again returned into the system.