NOVELTY - A separator (3) has base material formed by molding stainless alloy board to uneven-shaped wave type, and nitrated case formed in depth from surface of base material. Nitrated case has M4N-type crystal structure with which nitrogen atom is positioned at octahedron space based on face-centered cubic lattice of unit cells formed with transition metal atoms. Nitrated case has nitrated case (13a) formed at flat portion (13) of base material, and another nitrated case (14a) formed in surface of protrusions (14), which protrudes from portion (13).    USE - For fuel cell stack used as motive power source for fuel cell vehicle (both claimed) such as car (from drawings).    ADVANTAGE - The separator is economical, and has excellent corrosion resistance. The contact resistance between separator and electrode is low.    DETAILED DESCRIPTION - A separator (3) has a base material obtained by molding a stainless alloy board containing iron as a main component, and chromium, nickel or molybdenum, to uneven-shaped wave type, and nitrated case formed in depth from surface of base material. The nitrated case has M4N-type crystal structure containing iron as main component, with which nitrogen atom is positioned at octahedron space based on face-centered cubic lattice of unit cells formed with transition metal atoms chosen from iron, chromium, nickel and molybdenum. The nitrated case has a nitrated case (13a) formed at concave-portion groove-bottom (flat) portion (13) of base material, and another nitrated case (14a) formed in the surface of protrusion (14), which protrudes from the portion (13) of base material. An INDEPENDENT CLAIM is included for manufacture of separator, which involves providing plasma nitriding processing to base material, and forming nitrated case at surface layer of the base material.    DESCRIPTION OF DRAWING(S) - The figure shows the sectional view of separator positioned on both surfaces of single cell. (Drawing includes non-English language text)    Single cell (2)    Separator (3)    Flat portion (13)    Protrusions (14)    Nitrated cases (13a,14a)