NOVELTY - The shift reaction catalyst has a catalyst metal which promotes shift reaction which generates hydrogen and carbon dioxide from carbon monoxide and water vapor. The catalyst has water vapor adsorbing material (WVAM) which absorbs water vapor. Water vapor adsorbing material exists in equilibrium state, absorption state and discharge state.    USE - For use in fuel cell apparatus.    ADVANTAGE - The shift reaction catalyst effectively accelerates the shift reaction to form hydrogen and carbon dioxide from carbon monoxide and water vapor.    DETAILED DESCRIPTION - The shift reaction catalyst has a catalyst metal which promotes shift reaction which generates hydrogen and carbon dioxide from carbon monoxide and water vapor. The catalyst has water vapor adsorbing material (WVAM) which absorbs water vapor. WVAM in equilibrium state does not exchange water vapor between surroundings in preset conditions. WVAM in absorption state absorbs water vapor when surrounding steam partial pressure is higher than steam partial pressure of surrounding in equilibrium state. WVAM in discharge state emits water vapor when surrounding steam partial pressure is lower than steam partial pressure of surrounding in equilibrium state. INDEPENDENT CLAIMS are also included for the following: Carbon monoxide concentration reduction method, involves using shift-reaction catalyst which promotes shift reaction between water vapor supplied to the catalyst, and carbon monoxide in gas supplied to the catalyst; Carbon monoxide concentration reduction apparatus, comprising a shift portion equipped with shift reaction catalyst which accelerates the shift reaction, and a supply unit to supply gas and water vapor on shift reaction catalyst; Fuel cell apparatus comprising a fuel cell which obtains an electromotive force by an electrochemical reaction. The apparatus also comprises a modifier which modified the hydrocarbon group fuel to form hydrogen rich gas. The hydrogen rich gas from modifier is supplied to shift portion comprising shift reaction catalyst, and shift reaction is advanced between carbon monoxide contained in hydrogen rich gas, and water vapor supplied to the shift reaction catalyst. The shift portion reduces the concentration of carbon monoxide in hydrogen rich gas. The hydrogen gas is then supplied as heating gas to the fuel cell    DESCRIPTION OF DRAWING(S) - The figure shows the condition of shift catalyst. (Drawing includes non-English language text).