A method and a device for removing acidic materials, such as CO.sub.2 and H.sub.2S, with limited energy consumption are provided. The method comprises a step of introducing the feed gas into a first absorber, and removing CO.sub.2 and H.sub.2S from the feed gas by contacting the feed gas with a lean solution in the first absorber; and a step of introducing the feed gas into a second absorber, and removing CO.sub.2 and H.sub.2S remaining in the feed gas by contacting the feed gas with a semi-lean solution in the second absorber. The rich solution having absorbed CO.sub.2 and H.sub.2S in the first and second absorber is introduced into a flash drum where an internal pressure is kept lower than that in the first absorber and in the second absorber. After a part of CO.sub.2 and H.sub.2S is released from the rich solution in the flash drum to obtain a semi-lean solution, a part of the semi-lean solution is cooled and introduced into the second absorber to contact with the feed gas in the second absorber. A remaining part of the semi-lean solution is introduced into a stripper and heated to release remaining CO.sub.2 and H.sub.25 from the semi-lean solution and to obtain a lean solution. A part of the lean solution is cooled and introduced into the first absorber to contact with the feed gas in the first absorber. A remaining part of the lean solution is cooled, introduced into the second absorber at an upper level of the second absorber, and is contacted with the feed gas in the second absorber, and thereby obtaining a treated gas.