PURPOSE: To prevent escape of a low b.p. solvent to an absorbing tower by a method wherein a liquid storage part of a disorption tower is made large to provide a heating means and the low b.p. solvent dissolved in an absorbing liquid is released in said disorption tower.

CONSTITUTION: The liquid storage part 20 is provided to a tower bottom part of a diffusion tower 9 and a steam coil 21 is arranged therein as the heating means. In order to control the steam amount in the coil 21, the temp. of the liquid storage part is detected by a detecting means 22 and a valve 27 is adjusted so as to adjust said temp. to a predetermined temp. by a steam flow amount adjusting meter 23A and a control apparatus 24. A low b.p. solvent vapor from a line 23 and an absorbing liquid absorbing CO and subjected to countercurrent contact in a packing layer 10 to release a CO gas. The absorbing liquid after releasing CO flowed downwardly to the storage part is heated to a temp. of a b.p. or more of the solvent by the steam coil 21 and the solvent dissolvent into the absorbing liquid is released. The absorbing liquid from which CO and the solvent are removed is returned to the absorbing tower by a pump 25. A solvent vapor released from the absorbing liquid is again supplied to the packing layer 10 along with a solvent vapor 23 from a reboiler.