An exhaust gas purifying method for a fuel cell vehicle comprises preparing an exhaust gas purifying system for the fuel cell vehicle, the exhaust gas purifying system including a methane removal catalyst for accelerating the conversion of methane into hydrogen and carbon monoxide. The sorbent precursor is a NaHCO3-containing compound, and trona is preferred as the sorbent precursor. A judging device is electrically connected to the ultrasonic wave sensor for detecting a double feed of the sheets based upon an output signal from the wave receiving sensor at a predetermined time after the register roller starts rotating. The memory cell array includes the first and second memory cells disposed in intersections of the word line and bit line.