The system includes: an absorber which brings an introduction gas into contact with an absorbent that absorbs CO2 and H2S; an absorbent regenerator which releases CO2 or the like to regenerate the absorbent; a second supply line which returns a regenerated absorbent to the absorber from the regenerator; a third supply line which extracts a semi-rich solution from the vicinity of a middle stage of the absorber, and introduces the semi-rich solution to the vicinity of the middle stage of the regenerator; and a semi-rich solution heat exchanger which is interposed at an intersection between the third supply line and the second supply line to perform the heat exchange between the semi-rich solution and the lean solution.
