A carbon dioxide capture system comprising: an absorber having an absorption unit configured to cause carbon dioxide contained in exhaust gas to be treated to be absorbed in an absorbing liquid containing water; a stripper having a stripping unit configured to allow the carbon dioxide to be released from the absorbing liquid containing the carbon dioxide, the absorbing liquid being supplied from the absorber; a washing unit configured to use cleaning water to clean absorption unit exhaust gas discharged from the absorption unit of the absorber or stripping unit exhaust gas discharged from the stripping unit of the stripper; a gas-liquid separation device configured to cool washing unit exhaust gas discharged from the washing unit to generate condensed water, and separate the generated condensed water from the washing unit exhaust gas; a condensed water line configured to mix the condensed water into the cleaning water; a cleaning water line configured to mix the cleaning water into the absorbing liquid when the amount of the cleaning water is more than a predetermined amount; an absorbing liquid level gauge configured to measure liquid level of the absorbing liquid in the absorber or the stripper as a determination of the amount of water contained in the absorbing liquid; and a controller, wherein the condensed water line comprises a condensed water valve configured to regulate the amount of condensed water to be mixed, and the controller controls the condensed water valve so that opening degree of the condensed water valve is increased when the amount of water contained in the absorbing liquid as measured by the absorbing liquid level gauge is not more than a predetermined lower limit and that the opening degree of the condensed water valve is decreased when the amount of water contained in the absorbing liquid as measured by the absorbing liquid level gauge is not less than a predetermined upper limit. an absorber having an absorption unit configured to cause carbon dioxide contained in exhaust gas to be treated to be absorbed in an absorbing liquid containing water; a stripper having a stripping unit configured to allow the carbon dioxide to be released from the absorbing liquid containing the carbon dioxide, the absorbing liquid being supplied from the absorber; a washing unit configured to use cleaning water to clean absorption unit exhaust gas discharged from the absorption unit of the absorber or stripping unit exhaust gas discharged from the stripping unit of the stripper; a gas-liquid separation device configured to cool washing unit exhaust gas discharged from the washing unit to generate condensed water, and separate the generated condensed water from the washing unit exhaust gas; a condensed water line configured to mix the condensed water into the cleaning water; a cleaning water line configured to mix the cleaning water into the absorbing liquid when the amount of the cleaning water is more than a predetermined amount; an absorbing liquid level gauge configured to measure liquid level of the absorbing liquid in the absorber or the stripper as a determination of the amount of water contained in the absorbing liquid; and a controller, wherein the condensed water line comprises a condensed water valve configured to regulate the amount of condensed water to be mixed, and the controller controls the condensed water valve so that opening degree of the condensed water valve is increased when the amount of water contained in the absorbing liquid as measured by the absorbing liquid level gauge is not more than a predetermined lower limit and that the opening degree of the condensed water valve is decreased when the amount of water contained in the absorbing liquid as measured by the absorbing liquid level gauge is not less than a predetermined upper limit.