A desulfurization apparatus for desulfurizing a flue gas containing sulfur oxides through contact with a porous carbon material. The carbon material, which is provided in a desulfurization tower, is at least one species selected from activated carbon and activated carbon fiber. The apparatus contains an NO₂-gas-feeding apparatus for feeding NO₂ gas into the desulfurization tower. Within the desulfurization tower, a showering mechanism is provided at the top, the showering mechanism adjusting water content of the flue gas in the desulfurization tower to that corresponding to saturation with water vapor or higher at the treatment temperature.