A carbon monoxide treatment apparatus according to an exemplary embodiment of the present invention includes: a reactor body; a partitioning plate located inside the reactor body for partitioning an internal space of the reactor body into a first section and a second section; a channel member in the first section for transporting an introduced gas including a reformed gas and an oxidant gas to the second section; and a reaction unit around the channel member of the first section for reducing a concentration level of carbon monoxide in the introduced gas moving through the first section by utilizing a preferential oxidation reaction of the carbon monoxide and the oxidant gas of the introduced gas, wherein moisture of the introduced gas that has been partially condensed when passing through the channel member is stored in the second section.