Reducibility of a NiAl2O4 containing catalyst was studied. On a measurement of NiAl2O4 concentration in a catalyst, a peak area ratio of NiAl2O4 in XRD analysis was verified to express the NiAl2O4 concentration. The reducibility of NiAl2O4 was confirmed to be dependent on the calcining temperature to form NiAl2O4, not dependent on the calcining time. The catalyst containing NiAl2O4 was ascertained to be reduced under convenient conditions to actual plant operations; H-2/N-2 = 30/70 at 1023 K for 1 h + steam/CH4 = 6 at 1023 K for 17 h.