The formation of H.sub.2S in a stoichiometric or reducing atmosphere is restrained without using Ni or Cu as an environmental load substance. An additional oxide composed of an oxide of at least one kind of metal selected from the group consisting of Bi, Sn and Zn was added to a three-way catalyst for purifying an exhaust gas emitted from an internal combustion engine of which the combustion is controlled in near a stoichiometric atmosphere in the amount of from 0.02 mol to 0.2 mol per liter of the catalyst. The additional oxide forms SO.sub.3 or SO.sub.4 from SO.sub.2 in an oxidizing atmosphere, and stores sulfur components as a sulfide in a reducing atmosphere so that emission of H.sub.2S can be restrained. And since no environmental load substance is contained, the catalyst can be used safely.