According to the present invention, provided is a method of selectively removing carbon monoxide, comprising the step of preparing a catalyst bed capable of selectively oxidizing carbon monoxide and including a plurality of catalyst layers arranged in series and the plurality of catalyst layers differing from each other in the temperature of application and arranged in the order of the application temperature such that the catalyst layer having the lowest application temperature constitutes the upstream side of the catalyst bed, and the step of introducing a gaseous mixture containing H2, CO and an oxidizing agent of O2 into the catalyst bed through the upstream side of the catalyst bed and supplying an additional oxidizing agent to the gaseous mixture when the gaseous mixture is introduced into the catalyst layer having a high application temperature so as to selectively oxidize and remove CO from the gaseous mixture.