NOVELTY - A biological desulfurization apparatus comprises a reaction tower (1) into which biogas generated by anaerobic fermentation of organic waste is to be introduced, a carrier-packed layer (2a, 2b) arranged in the reaction tower and provided with a carrier to which microorganisms have adhered, an air feeder (3) that mixes air into a lower part of the reaction tower, and a sprinkling mechanism (7) that sprinkles water on an upper part of the reaction tower, where the carrier-packed layer is arranged in at least two stages.    USE - As biological desulfurization apparatus (claimed) for biogas generated by anaerobic digestive treatment of organic discharged water such as sewage and industrial drainage.    ADVANTAGE - The biological desulfurization apparatus for biogas, prevents clogging in the carrier-packed layer and holds microorganisms adhering to the carrier, thus enabling stable treatment. The packed layer is divided into packed layers, to provide the apparatus with several packed layers, thus allowing spaces among the packed layers to serve as gas buffers with which the disproportional flow rate of biogas is lessened. Clogging in the packed layer is thus prevented and the ability of the apparatus to remove hydrogen sulfide is stabilized. The diameter of the carrier in the carrier-packed layer at the lower-stage side is preferably larger than the diameter of the carrier in the carrier-packed layer at the upper-stage side. By increasing gaps in the carrier-packed layer at the lower-stage side in this manner, the period up to clogging can be prolonged. Thus by reducing the frequency of washing, the amount of microorganisms adhering to the carrier-packed layer at the lower-stage side can be increased to improve the efficiency of treatment. An air pipe for washing is arranged preferably in each of the carrier-packed layers, thus constituting the apparatus such that the carrier-packed layers can be washed separately from one another. The lower part where solids are easily accumulated, or the upper part, can thus solely be washed. The reaction tower can be prevented from clogging, and the clogged carrier-packed layer can solely be washed, thus preventing the deterioration in treatment performance caused by a deficiency of microorganisms after washing.    DETAILED DESCRIPTION - A biological desulfurization apparatus comprises a reaction tower (1) into which biogas generated by anaerobic fermentation of organic waste is to be introduced, a carrier-packed layer (2a, 2b) arranged in the reaction tower and provided with a carrier to which microorganisms have adhered, an air feeder (3) that mixes air into a lower part of the reaction tower, and a sprinkling mechanism (7) that sprinkles water on an upper part of the reaction tower, where the carrier-packed layer is arranged in at least two stages, where the diameter of the carrier in the carrier-packed layer at the lower-stage side is larger than the diameter of the carrier in the carrier-packed layer at the upper-stage side. An air pipe for washing is arranged in each of the carrier-packed layers. A sprinkling mechanism is arranged in every carrier-packed layer or in every predetermined number of carrier-packed layers. Several carrier-packed layers are further provided in an intermediate portion with an intermediate air feeder which introduces air. The amount of water to be sprinkled from the sprinkling mechanism nearer to the side of biogas inflow is increased.    DESCRIPTION OF DRAWING(S) - The figure shows skeleton framework of the biogas biological desulfurization apparatus.    Reaction tower (1)    Carrier-packed layer (2a, 2b)    Air feeder (3)    Washing air pipes (6a, 6b)    Sprinkling mechanism (7)