To perform efficient treatment under good environment by preventing the diffusion of hydrogen sulfide, in reducing the use amount of alkali for adjusting the pH of an absorbing solution by removing carbon dioxide in the absorbing solution, in a method wherein hydrogen sulfide-containing gas is introduced into a gas-liquid contact tower to absorb and remove hydrogen sulfide in the gas and the absorbing solution having absorbed hydrogen sulfide is introduced into an oxidation tank to aerobically oxidize and decompose sulfide in the solution by microorganisms.

In the biological desulfurization method, the hydrogen sulfide-containing gas is introduced into the gas-liquid contact tower to be brought into contact with the absorbing solution to absorb hydrogen sulfide in the raw gas by the absorbing solution, and the obtained absorbing solution is aerobically oxidized and decomposed by microorganisms and subsequently subjected to decarbonization treatment while the decaronized treated water is circulated and used as the absorbing solution. The biological desulfurization apparatus is equipped with the gas-liquid contact tower 2, for bringing the hydrogen sulfide-containing gas into contact with the absorbing solution, the oxidation tank 4 equipped with an aeration means 7 receiving the absorbing solution discharged from the gas-liquid contact tower 2 and oxidizing and decomposing sulfide in the absorbing solution, a decarbonation tank 9 for applying decarbonation treatment to the treated water of the oxidation tank 4 and a means 15 for circulating and supplying a part of the treated water of the decarbonation tank 9 to the gas-liquid contact tower 2 as the absorbing solution.