NOVELTY - A separator (3) has a base layer (13), a nitrated case (15) formed on layer (13), a nitrated case (16) containing chromium nitride formed on case (15), and an oxidizing layer (17) having thickness of 15 nm or less formed on case (16). The base layer contains iron, and is obtained using stainless steel containing chromium, nickel and/or molybdenum. The nitrated case (15) contains iron as main component, and has transition metal atom nitride type crystal structure in which nitrogen atom is arranged at octahedron space based on face-centered cubic lattice.    USE - For polymer electrolyte type fuel cell used as power supply for motor vehicle and fuel cell vehicle (claimed).    ADVANTAGE - The separator is economical and has excellent corrosion resistance. The fuel cell stack has reduced size and is economical.    DETAILED DESCRIPTION - A separator has a base layer (13), a nitrated case (15) formed on the base layer, a nitrated case (16) containing chromium nitride formed on the case (15), and an oxidizing layer (17) having thickness of 15 nm or less formed on the case (16). The base layer contains iron as main component, and is obtained using stainless steel containing chromium, nickel and/or molybdenum. The nitrated case (15) contains iron as main component, and has transition metal atom nitride (M4N) type crystal structure in which nitrogen atom is arranged at octahedron space based on face-centered cubic lattice, where M is iron, chromium, nickel and/or molybdenum. INDEPENDENT CLAIMS are included for the following:    (1) manufacture of separator. Plasma nitridation of stainless steel is carried out, and nitrated case (15) is formed. Then, nitrated case (16) is directly formed on the nitrated case (15) by plasma nitridation. Oxidizing layer is formed on the case (16) to obtain separator;    (2) fuel cell stack, which is obtained using separator; and    (3) fuel cell vehicle, which has fuel cell stack.    DESCRIPTION OF DRAWING(S) - The figure shows the perspective view and sectional view of separator. (Drawing includes non-English language text)    Separator (3)    Path of oxidizing agent (12)    Base layer (13)    Nitrated cases (15,16)    Oxidizing layer (17)