A wet type flue-gas desulfurization apparatus includes a desulfurization apparatus main body; a gas introducing unit that is disposed on a side wall of the desulfurization apparatus main body and that introduces a flue gas; an absorbent accumulating unit that accumulates an absorbent which has absorbed the sulfur oxide present in the flue gas; a circulation line that circulates the absorbent from the absorbent circulating unit; a spray pipe that is disposed in the vicinity of the middle portion of the desulfurization apparatus main body and that sprays the absorbent, which is circulated in the circulation line, as a spray liquid from a nozzle; an ORP meter that measures the oxidation reduction potential of the absorbent; and an oxidation resistant pipe group that, in the vicinity of the interface of the absorbent present in the absorbent accumulating unit, cushions a falling liquid falling from an absorber of the absorbent.