A CO 2 recovering apparatus includes a CO 2 absorber (16) that brings flue gas containing CO 2 into contact with CO 2 absorbent to reduce the CO 2 contained in the flue gas; and a regenerator (18) that reduces CO 2 contained in rich solvent absorbing CO 2 to regenerate the rich solvent, so that lean solvent that is the CO 2 absorbent having the CO 2 reduced in the regenerator (18) is reused in the CO 2 absorber (16). The CO 2 recovering apparatus further includes a controller that detects the difference between the gas temperature (T 1 ) of the flue gas guided into the entrance of the CO 2 absorber (16) and the gas temperature (T 2 ) of the gas exiting the CO 2 absorber (16), and the absorbent concentration (X (Vol%)) of the CO 2 absorbent; and controls to adjust the amount of water contained in the gas depending on the gas temperature difference between the gas entering and the gas exiting the CO 2 absorber (16) and to keep the absorbent concentration of the CO 2 absorbent within a set range (e.g., X 0 ±10% in a relative ratio).