A CO 2 recovery device comprising: an absorption tower configured to bring an emission gas including CO 2 in contact with an absorbent solution so as to remove the CO 2 from the emission gas, thus generating a rich solution corresponding to the absorbent solution having absorbed the CO 2; a regeneration tower configured to regenerate the absorbent solution by removing the CO 2 from the rich solution; a heat exchanger configured to carry out heat exchange between the rich solution and the regenerated absorbent solution which is higher in temperature than the rich solution; a rich-solution delivery pipe (53, 54) configured to deliver the rich solution from the absorption tower to the regeneration tower through the heat exchanger; an absorbent-solution delivery pipe (51, 52) configured to deliver the absorbent solution from the regeneration tower to the absorption tower through the heat exchanger; a bypass pipe configured to deliver the rich solution before the heat exchanger to the absorbent-solution delivery pipe via a bypass control valve; a rich-solution control valve configured to adjust a flow rate of the rich solution flowing through the rich-solution delivery pipe after the heat exchanger toward the regeneration tower; and a level gauge configured to measure a liquid level of the absorbent solution accumulated in the base of the regeneration tower, wherein an opening of the rich-solution control valve is increased according to a reduction of the liquid level when a change rate of the liquid level shows an increasing trend, wherein the opening of the bypass control valve is increased according to a reduction of the liquid level when the change rate of the liquid level shows a deceasing trend. an absorption tower configured to bring an emission gas including CO 2 in contact with an absorbent solution so as to remove the CO 2 from the emission gas, thus generating a rich solution corresponding to the absorbent solution having absorbed the CO 2; a regeneration tower configured to regenerate the absorbent solution by removing the CO 2 from the rich solution; a heat exchanger configured to carry out heat exchange between the rich solution and the regenerated absorbent solution which is higher in temperature than the rich solution; a rich-solution delivery pipe (53, 54) configured to deliver the rich solution from the absorption tower to the regeneration tower through the heat exchanger; an absorbent-solution delivery pipe (51, 52) configured to deliver the absorbent solution from the regeneration tower to the absorption tower through the heat exchanger; a bypass pipe configured to deliver the rich solution before the heat exchanger to the absorbent-solution delivery pipe via a bypass control valve; a rich-solution control valve configured to adjust a flow rate of the rich solution flowing through the rich-solution delivery pipe after the heat exchanger toward the regeneration tower; and a level gauge configured to measure a liquid level of the absorbent solution accumulated in the base of the regeneration tower, wherein an opening of the rich-solution control valve is increased according to a reduction of the liquid level when a change rate of the liquid level shows an increasing trend, wherein the opening of the bypass control valve is increased according to a reduction of the liquid level when the change rate of the liquid level shows a deceasing trend.