A hydraulic working oil composition for buffers which comprises:a lubricating oil as a base oil,(A) at least one phosphorus-containing compound selected from the group consisting of a phosphoric acid ester having a specific structure, a phosphorous acid ester having a specific structure and a salt of-the phosphoric acid ester and/or the phosphorous acid ester with an aliphatic monoamine having 8-22 carbon atoms, and(B) at least one nitrogen-containing compound selected from the group consisting of an aliphatic polyamine having a specific structure and a salt of the aliphatic polyamine with an aliphatic acid having 6 carbon atoms, the compounds (A) and (B) being essential components added to said base oil.