Complete oxidation of 2,000 ppm CO in H-2 is attained over 10 wt.% Pt/CNT (carbon nano-tube) catalyst (0.019 g) at room temperature by adding 2,000 ppm O-2 to hydrogen flowing at 100 mL/min. By insetting 5 wt.% Pt/CNT catalyst (0.8 g) in front of a PEFC (polymer electrolyte hydrogen fuel cell), the PEFC generated maximum wattage of 0.45 V x 0.75 A/cm(2) with no suppression for more than 7 h in a flow of H-2 (400 mL/min) containing 1,000 ppm CO. This result suggests a possibility of the hydrogen fuel cell operating in the shift gas.