in electric power generation if its h 2 s content can be reduced for example to 5 ppm or less the resulting combustion exhaust gas will have an so x concentration of 1 ppm or less this means that almost perfect desulfurization can be achieved in substance in the case of gas for domestic use it is necessary from the viewpoint of safety to reduce its h 2 s content to 10 ppm or less and preferably to substantially less than its detection limit thus the h 2 s contents of object gases used for certain purposes need to be reduced significantly in such object gases co 2 is usually contained in a larger amount than h 2 s according to the first aspect of the present invention such an object gas is treated with an excess of an aqueous solution of a hindered amine comprising a di lower alkyl amino lower alkanol or triethylenediamine although the aqueous solution absorbs some co 2 it absorbs h 2 s with relatively high selectivity so that the h 2 s content in the treated gas is markedly reduced no particular limitation is placed on such object gases and the h 2 s content in the treated gas can be reduced to 10 ppm or less and preferably to substantially less than its detection limit by choosing the absorbing conditions properly according to the composition of the object gas thus the above described need for a reduction in h.