PURPOSE:To maintain high desulfurizing performance of a desulfurizer even when using semicoke as an adsorbent by making the desulfurizer a moving bed type. CONSTITUTION:While moving the semicoke as an adsorbent, supplied from conduit 24, from the upper part to the lower part of the moving bed type desulfurizing tower 101, SOx present in the waste gas from conduit 4 is adsorbed on the semicoke. Then, the semicoke is sent to the upper part of a moving bed type regenerating tower 104 through conduit 16 to desorb SOx from the semicoke, screened by a classifier, and then recycled to the desulfurizer tower 101, where fine semicoke is retuned through conduit 5 to a boiler 100 and a corresponding amount of fresh semicoke is supplied from the conduit 24. The desulfurized waste gas is discharged from a stack 108, and the desorbed gas in the regenerating tower is sent to a reducing tower 105 and then cooled in a condenser 106 to remove crude sulfur. Furthermore, the concentration of SOx present in waste gas before and behind of the desulfurizer is detected to control the moving amount of semicoke in order to keep the desulfurization rate constant.