As the first step to understand the electrode impedance at gas, electrode/solid-electrolyte systems, the complete capturing of electrode impedance at H-2, Ni(NiO)/stabilized zirconia was conducted with an empirical equivalent circuit proposed for O-2, Pt/stabilized zirconia. Impedance plots of various depressed semicircles and those that overlapped were completely duplicated with the circuit and compacted into values of three parameters for the impedance at the electrode process and two parameters for a diffusion through a porous layer. The former three were affected by the temperature and the partial pressure of H2O but not by the thickness of the electrode. It was suggested that the impedance plot of a single depressed semicircle may sometimes contain relatively large diffusion impedance.