A CO 2 recovering apparatus (10A, 10B, 10C) comprising: a cooling tower for allowing an exhaust gas containing CO 2 to contact water so as to cool the exhaust gas; a CO 2 absorber including a CO 2 recovering unit for allowing a CO 2 absorbing solution that absorbs CO 2 to contact the exhaust gas, so as to eliminate CO 2 from the exhaust gas; an absorbing solution regenerator for releasing CO 2 from the CO 2 absorbing solution having absorbed CO 2 so as to regenerate the CO 2 absorbing solution; an absorbing solution level meter for measuring a liquid level of the CO 2 absorbing solution at a tower bottom of the CO 2 absorber; and a level controller for performing automatic control for one or both of a supply amount of makeup water to be supplied to the CO 2 absorber and a condensation amount of water contained in the exhaust gas, based on the liquid level of the CO 2 absorbing solution detected by the absorbing solution level meter, wherein while the gas supply amount of the exhaust gas supplied to the CO 2 absorber measured by gas flowmeter is constant, said level controller performs the automatic control for stably keeping the concentration of the CO2 absorbing solution; according to the automatic control, the accumulation amount of the CO 2 absorbing solution in the CO 2 recovering unit, the supply amount of the makeup water, and the liquid level of the rich solution accumulated in the liquid pool at the tower bottom of the CO 2 absorber 12 are constant; when the supply amount of the exhaust gas increases the automatic control provides that the set value of liquid level of the rich solution varies based on a set relationship between the gas supply amount of the exhaust gas and the set value of the liquid level, the accumulation amount of the CO 2 absorbing solution in the CO 2 recovering unit increases, the supply amount of the makeup water is adjusted, so that the concentration of the CO 2 absorbing solution 16 is maintained at a constant level. a cooling tower for allowing an exhaust gas containing CO 2 to contact water so as to cool the exhaust gas; a CO 2 absorber including a CO 2 recovering unit for allowing a CO 2 absorbing solution that absorbs CO 2 to contact the exhaust gas, so as to eliminate CO 2 from the exhaust gas; an absorbing solution regenerator for releasing CO 2 from the CO 2 absorbing solution having absorbed CO 2 so as to regenerate the CO 2 absorbing solution; an absorbing solution level meter for measuring a liquid level of the CO 2 absorbing solution at a tower bottom of the CO 2 absorber; and a level controller for performing automatic control for one or both of a supply amount of makeup water to be supplied to the CO 2 absorber and a condensation amount of water contained in the exhaust gas, based on the liquid level of the CO 2 absorbing solution detected by the absorbing solution level meter, wherein while the gas supply amount of the exhaust gas supplied to the CO 2 absorber measured by gas flowmeter is constant, said level controller performs the automatic control for stably keeping the concentration of the CO2 absorbing solution; according to the automatic control, the accumulation amount of the CO 2 absorbing solution in the CO 2 recovering unit, the supply amount of the makeup water, and the liquid level of the rich solution accumulated in the liquid pool at the tower bottom of the CO 2 absorber 12 are constant; when the supply amount of the exhaust gas increases the automatic control provides that the set value of liquid level of the rich solution varies based on a set relationship between the gas supply amount of the exhaust gas and the set value of the liquid level, the accumulation amount of the CO 2 absorbing solution in the CO 2 recovering unit increases, the supply amount of the makeup water is adjusted, so that the concentration of the CO 2 absorbing solution 16 is maintained at a constant level.