NOVELTY - Carbon monoxide (CO) concentration in hot gas containing H and CO is reduced. Two reaction chambers containing catalysts that selectively oxidize CO at high and low temperatures, respectively, are provided. Air for oxidation is supplied near high temperature catalyst, so that a low temperature-distribution is formed in upstream chamber and a high temperature-distribution is formed in downstream chamber.    USE - For fuel cell, especially solid polymer fuel cell (PEFC) used in electric vehicle.    ADVANTAGE - Selective removal of carbon monoxide is enabled in a short time. Carbon monoxide concentration is made extremely low by reduction in a wide temperature range, so that poisoning of anode catalyst of solid polymer fuel cell (PEFC) is prevented and the cell can be easily mounted on motor vehicles. The apparatus is made compact.    DETAILED DESCRIPTION - A carbon monoxide selective removal apparatus reduces carbon monoxide (CO) concentration in hot gas containing hydrogen (H) and CO. Two connected reaction chambers are provided. The upstream side reaction chamber is filled with a high temperature catalyst which performs selective oxidation of CO at a high temperature, and the downstream side reaction chamber is filled with a low temperature catalyst which oxidizes CO selectively at a lower temperature. A cooling unit to cool the catalysts in both chambers, is provided. An air supply line supplies air for oxidation, and is arranged near the high temperature catalyst, so that a low temperature-distribution is formed in the upstream side chamber and a high temperature-distribution is formed in the downstream side chamber.    An INDEPENDENT CLAIM is also included for the selective carbon monoxide removal method for hot fuel gas supplied to fuel cell. The oxygen concentration in the high temperature catalyst side is increased by the supply of air, which also enables to cool the catalysts in both chambers, and to maintain a high and low temperature-distribution within the catalysts in the chambers, respectively.