To fix and recover gaseous carbon monoxide by making carbon monoxide adsorbed to an organometallic complex having an one- or three-dimensional channel structure as an adsorbing material and separating/removing the carbon monoxide from a subject material to be treated.

A gas treating device 1 is composed freely selectively of the first separation state in which the gas to be treated (gaseous hydrogen) is introduced to a adsorbing material housing chamber 3 whose pressure is set to make the carbon monoxide adsorbed to the adsorbing material, and also a residual gas is introduced to the first recovering passage 5 to be captured and the second separation state in which the carbon monoxide adsorbed to the adsorbing material 2 is desorbed and introduced to the second recovering passage 6 to be captured or to be released to atmosphere. the organometallic complex having the one- or three-dimensional channel structure is a asorbing material for the treatment which separates, removes, recovers, etc., the gaseous carbon monoxide from other gas, and when copper is incorporated into the organometallic complex as a metal, more strong separating capacity and recovering capacity are obtained since a copper carbonyl complex is formed between the carbon monoxide and the complex.