A CO 2 recovery apparatus (10C; 10D; 10E) comprising: an absorber that brings flue gas containing CO 2 into counter-current contact with CO 2 absorbent to reduce CO 2, and a regenerator that regenerates rich solution that has absorbed CO 2 through heat exchange, in which lean solution having CO 2 reduced in the regenerator is reused in the absorber, wherein the absorber includes at least one CO 2 absorbing unit that recovers CO 2 in the flue gas containing CO 2, the CO 2 recovery apparatus (10C; 10D; 10E) being characterized by including: a heat exchanger that is arranged in an absorbent circulating line; an upper-stage CO 2 absorbing unit (1010-U) and a lower-stage CO 2 absorbing unit (1010-L), and the CO 2 recovery apparatus (10C; 10D) further comprises: an absorbent extracting line through which CO 2 absorbent is extracted from a lower side of the upper-stage CO 2 absorbing unit (1010-U), wherein the absorbent circulating line connects a lower side of the lower-stage CO 2 absorbing unit (1010-L) and an upper side of the lower-stage CO 2 absorbing unit (1010-L) to supply the lower-stage CO 2 absorbing unit (1010-L) with the CO 2 absorbent extracted from the lower side of the lower-stage CO 2 absorbing unit (1010-L) merged with the CO 2 absorbent extracted from the lower side of the upper-stage CO 2 absorbing unit (1010-U) and wherein the heat exchanger is configured to cool the CO 2 absorbent extracted from the lower side of the lower-stage CO 2 absorbing unit (1010-L) before or after the CO 2 absorbent extracted from the lower side of the upper-stage CO 2 absorbing unit (1010-U) via the absorbent extracting line is merged with the CO 2 absorbent extracted from the lower side of lower stage CO2 absorbing unit (1010-L). an absorber that brings flue gas containing CO 2 into counter-current contact with CO 2 absorbent to reduce CO 2, and a regenerator that regenerates rich solution that has absorbed CO 2 through heat exchange, in which lean solution having CO 2 reduced in the regenerator is reused in the absorber, wherein the absorber includes at least one CO 2 absorbing unit that recovers CO 2 in the flue gas containing CO 2, a heat exchanger that is arranged in an absorbent circulating line; an upper-stage CO 2 absorbing unit (1010-U) and a lower-stage CO 2 absorbing unit (1010-L), and the CO 2 recovery apparatus (10C; 10D) further comprises: an absorbent extracting line through which CO 2 absorbent is extracted from a lower side of the upper-stage CO 2 absorbing unit (1010-U), wherein the absorbent circulating line connects a lower side of the lower-stage CO 2 absorbing unit (1010-L) and an upper side of the lower-stage CO 2 absorbing unit (1010-L) to supply the lower-stage CO 2 absorbing unit (1010-L) with the CO 2 absorbent extracted from the lower side of the lower-stage CO 2 absorbing unit (1010-L) merged with the CO 2 absorbent extracted from the lower side of the upper-stage CO 2 absorbing unit (1010-U) and wherein the heat exchanger is configured to cool the CO 2 absorbent extracted from the lower side of the lower-stage CO 2 absorbing unit (1010-L) before or after the CO 2 absorbent extracted from the lower side of the upper-stage CO 2 absorbing unit (1010-U) via the absorbent extracting line is merged with the CO 2 absorbent extracted from the lower side of lower stage CO2 absorbing unit (1010-L).