A CO 2 recovery unit (10A; 10B; 10C) comprising: a CO 2 absorber configured to bring a CO 2 -containing flue gas containing CO 2 into contact with a CO 2 -absorbent to remove CO 2; and a CO 2 -absorbent regenerator configured to separate CO 2 from the CO 2 -absorbent that has absorbed CO 2 therein and to regenerate the CO 2 -absorbent; the CO 2 recovery unit (10A; 10B; 10C) being configured so that the CO 2 absorber reutilizes a lean solution obtained by removing CO 2 in the CO 2 -absorbent regenerator, the CO 2 absorber comprising: a CO 2 -absorbing unit that absorbs CO 2 in a CO 2 -containing flue gas with the CO 2 -absorbent; a main water rinsing unit that is provided on a gas flow downstream side of the CO 2 -absorbing unit and that uses rinsing water to recover the accompanying CO 2 -absorbent while cooling decarbonated flue gas; a circulation line (L 1) that supplies the rinsing water containing the CO 2 -absorbent recovered in a liquid reservoir in the main water rinsing unit from a top portion side in the main water rinsing unit, and circulates the rinsing water; a preliminary water rinsing unit provided between the CO 2 -absorbing unit and the main water rinsing unit, a withdrawal line (L 2) that withdraws a portion of the rinsing water, and a cooling unit that is provided on the withdrawal line (L 2) and cools the portion of the withdrawn rinsing water, the CO 2 absorber being configured to: withdraw the portion of the rinsing water containing the CO 2 -absorbent from the main water rinsing unit, supply the portion of the rinsing water into the preliminary water rinsing unit from the main water rinsing unit side through the withdrawal line (L 2) to preliminarily rinse the CO 2 -absorbent that accompanies the flue gas, and recover the CO 2 -absorbent; and allow the preliminary rinsing water obtained by the preliminary rinsing to meet with the CO 2 -absorbent through the CO 2 -absorbing unit, bring into countercurrent contact with the flue gas and directly flow down on a lower side of the CO 2 -absorbing unit. a CO 2 absorber configured to bring a CO 2 -containing flue gas containing CO 2 into contact with a CO 2 -absorbent to remove CO 2; and a CO 2 -absorbent regenerator configured to separate CO 2 from the CO 2 -absorbent that has absorbed CO 2 therein and to regenerate the CO 2 -absorbent; the CO 2 recovery unit (10A; 10B; 10C) being configured so that the CO 2 absorber reutilizes a lean solution obtained by removing CO 2 in the CO 2 -absorbent regenerator, the CO 2 absorber comprising: a CO 2 -absorbing unit that absorbs CO 2 in a CO 2 -containing flue gas with the CO 2 -absorbent; a main water rinsing unit that is provided on a gas flow downstream side of the CO 2 -absorbing unit and that uses rinsing water to recover the accompanying CO 2 -absorbent while cooling decarbonated flue gas; a circulation line (L 1) that supplies the rinsing water containing the CO 2 -absorbent recovered in a liquid reservoir in the main water rinsing unit from a top portion side in the main water rinsing unit, and circulates the rinsing water; a preliminary water rinsing unit provided between the CO 2 -absorbing unit and the main water rinsing unit, a withdrawal line (L 2) that withdraws a portion of the rinsing water, and a cooling unit that is provided on the withdrawal line (L 2) and cools the portion of the withdrawn rinsing water, a CO 2 -absorbing unit that absorbs CO 2 in a CO 2 -containing flue gas with the CO 2 -absorbent; a main water rinsing unit that is provided on a gas flow downstream side of the CO 2 -absorbing unit and that uses rinsing water to recover the accompanying CO 2 -absorbent while cooling decarbonated flue gas; a circulation line (L 1) that supplies the rinsing water containing the CO 2 -absorbent recovered in a liquid reservoir in the main water rinsing unit from a top portion side in the main water rinsing unit, and circulates the rinsing water; a preliminary water rinsing unit provided between the CO 2 -absorbing unit and the main water rinsing unit, a withdrawal line (L 2) that withdraws a portion of the rinsing water, and a cooling unit that is provided on the withdrawal line (L 2) and cools the portion of the withdrawn rinsing water, the CO 2 absorber being configured to: withdraw the portion of the rinsing water containing the CO 2 -absorbent from the main water rinsing unit, supply the portion of the rinsing water into the preliminary water rinsing unit from the main water rinsing unit side through the withdrawal line (L 2) to preliminarily rinse the CO 2 -absorbent that accompanies the flue gas, and recover the CO 2 -absorbent; and allow the preliminary rinsing water obtained by the preliminary rinsing to meet with the CO 2 -absorbent through the CO 2 -absorbing unit, bring into countercurrent contact with the flue gas and directly flow down on a lower side of the CO 2 -absorbing unit. withdraw the portion of the rinsing water containing the CO 2 -absorbent from the main water rinsing unit, supply the portion of the rinsing water into the preliminary water rinsing unit from the main water rinsing unit side through the withdrawal line (L 2) to preliminarily rinse the CO 2 -absorbent that accompanies the flue gas, and recover the CO 2 -absorbent; and allow the preliminary rinsing water obtained by the preliminary rinsing to meet with the CO 2 -absorbent through the CO 2 -absorbing unit, bring into countercurrent contact with the flue gas and directly flow down on a lower side of the CO 2 -absorbing unit.