NOVELTY - A separator (3) has nitrated layer (15) formed on base layer (13), and nitrated layer (16) formed on nitrated layer (15). The nitrated layer (16) is single layer of chromium nitride, compound layer of chromium nitride and metal nitride type crystal structure, or bi-layered nitrated layer. The nitrated layer (15) contains iron as main component, and has metal nitride type crystal structure, in which nitrogen atom is arranged at octahedron space based on unit cells of face-centered cubic lattice formed with transition metal atom.    USE - For fuel cell stack of fuel cell vehicle (both claimed).    ADVANTAGE - The separator has excellent corrosion resistance, and is economical. The nitrated layer has high chemical stability.    DETAILED DESCRIPTION - A separator has nitrated layer (15) formed on a base layer, and a nitrated layer (16) formed on nitrated layer (15). The layer (16) is separated from base layer. The nitrated layer (16) is single layer of chromium nitride, compound layer of chromium nitride and metal nitride (M4N) type crystal structure, or bi-layered nitrated layer consisting of interface layer of chromium nitride and M4N-type crystal structure, and chromium nitride layer formed on interface layer. The base layer is formed using stainless steel having iron as main component and containing chromium, and nickel or molybdenum. The nitrated layer (15) contains iron as main component, and has M4N type crystal structure, in which nitrogen atom is arranged at octahedron space based on unit cells of face-centered cubic lattice formed with transition metal atom chosen from iron, chromium, nickel and molybdenum. INDEPENDENT CLAIMS are included for the following:    (1) manufacture of separator;    (2) fuel cell stack, which has the separator; and    (3) fuel cell vehicle, to which fuel cell stack is mounted.    DESCRIPTION OF DRAWING(S) - The figure shows the perspective view and sectional view of separator. (Drawing includes non-English language text)    Separator (3)    Upper surface (11)    Channel (12)    Base layer (13)    Nitrated layers (15,16)