A wet flue gas desulfurization apparatus comprising: an absorber that includes an absorbent storage tank for storing an absorbent and a flue gas passage through which flue gas discharged from a combustor passes, the absorber being configured to bring the flue gas into contact with the absorbent to cause the absorbent to absorb a sulfur oxide included in the flue gas; a gas introduction unit that is arranged on an upper side wall of the absorber, and that is configured to introduce the flue gas into the absorber; an absorbent jetting unit that is arranged in the flue gas passage, and that is configured to jet the absorbent into a space of the absorber; an absorbent circulation line (L 11) that is configured to supply the absorbent to the absorbent jetting unit from the absorbent storage tank; an absorbent supply line (L 22) and an absorbent branch line (L 23) configured to supply part of the absorbent in the absorbent circulation line (L 11) to the water flow oxidation devices; a plurality of water flow oxidation devices that are configured to jet part of the absorbent branched and introduced from the absorbent circulation line (L 11) into an inside of the absorbent storage tank together with air; and a control device that is configured to adjust any one or both of the jetting amount of the absorbent jetted from the water flow oxidation device by executing any one or both of control for varying the number of the operating water flow oxidation devices and control for varying a circulation amount of the absorbent circulated into the water flow oxidation device, and the supply amount of the air supplied to the water flow oxidation device by executing control for varying an amount of the air supplied to the water flow oxidation device with an opening/closing valve based on the concentration of the sulfur compound in the absorbent within the absorbent storage tank, wherein the control device is configured to execute control for reducing the number of operating water flow oxidation devices when the concentration of the sulfur compound in the absorbent within the absorbent storage tank is lower than the predetermined threshold set in advance. an absorber that includes an absorbent storage tank for storing an absorbent and a flue gas passage through which flue gas discharged from a combustor passes, the absorber being configured to bring the flue gas into contact with the absorbent to cause the absorbent to absorb a sulfur oxide included in the flue gas; a gas introduction unit that is arranged on an upper side wall of the absorber, and that is configured to introduce the flue gas into the absorber; an absorbent jetting unit that is arranged in the flue gas passage, and that is configured to jet the absorbent into a space of the absorber; an absorbent circulation line (L 11) that is configured to supply the absorbent to the absorbent jetting unit from the absorbent storage tank; an absorbent supply line (L 22) and an absorbent branch line (L 23) configured to supply part of the absorbent in the absorbent circulation line (L 11) to the water flow oxidation devices; a plurality of water flow oxidation devices that are configured to jet part of the absorbent branched and introduced from the absorbent circulation line (L 11) into an inside of the absorbent storage tank together with air; and a control device that is configured to adjust any one or both of the jetting amount of the absorbent jetted from the water flow oxidation device by executing any one or both of control for varying the number of the operating water flow oxidation devices and control for varying a circulation amount of the absorbent circulated into the water flow oxidation device, and the supply amount of the air supplied to the water flow oxidation device by executing control for varying an amount of the air supplied to the water flow oxidation device with an opening/closing valve based on the concentration of the sulfur compound in the absorbent within the absorbent storage tank, wherein the control device is configured to execute control for reducing the number of operating water flow oxidation devices when the concentration of the sulfur compound in the absorbent within the absorbent storage tank is lower than the predetermined threshold set in advance.