NOVELTY - A biological desulfurization apparatus comprises biological reaction tank (1) into which a hydrogen sulfide gas-containing gas is introduced, carrier-packed layer (2ab) in the reaction tank and packed with carrier for adhesion of microorganisms, feeding mechanism that feeds an oxygen-containing gas to the reaction tank, and greater than or equal to 2 sprinkling mechanisms that sprinkle water for the organisms on upper part of the reaction tank.    USE - Biological desulfurization apparatus for treatment of organic drainage, including sewage and industrial drainage.    ADVANTAGE - The apparatus is rapidly started up, thus effective utilization of biogas in boiler or in electric generator is achieved because problems such as corrosion attributable to concentration of hydrogen sulfide in the gas is avoided. It is capable of achieving rapid start-up and stable treatment after start-up, and avoids clogging of sprinkling unit.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method of starting up the biological desulfurization apparatus, comprising starting up the apparatus while microorganisms are allowed to adhere to a carrier by feeding hydrogen sulfide-containing gas and oxygen-containing gas to biological reaction tank (1) under circulation of microorganism-containing liquid or sludge. The apparatus has first and second sprinkling mechanisms (3, 4). The first sprinkling mechanism has circulation tank, circulation pump, and pipe for introducing microorganism-containing liquid or sludge as seed sludge for biological desulfurization and circulating it through the reaction tank. In the first sprinkling mechanism, the pipe for connecting the circulation tank to the reaction tank extends to an inside of the reaction tank, and an extending portion of the pipe has a hole of 5-20 mm in diameter. The second sprinkling mechanism is on top of the reaction tank and is provided with pipe for sprinkling water on the carrier-packed layer. The pipe in the second sprinkling mechanism extends to the inside of the reaction tank, and the extending portion of the pipe has nozzle (11) excellent in ability to disperse water.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view of the biological desulfurization apparatus.    Biological reaction tank (1)    Carrier-packed layer (2ab)    First and second sprinkling mechanisms (3, 4)    Nozzle (11)    Detector (23)