NOVELTY - A transition metal nitride has layer (A) (11b) and layer (B) (11c) formed on base layer (12) of base material (10). The layer (A) has laminated crystal structure of nanometer-level containing nitride having specific type of cubic crystal structure, nitride having specific type of hexagonal crystal structure, or nitride having specific type of crystal structure. The layer (B) is formed from surface of base material along depth direction.    USE - Transition metal nitride used for manufacturing separator for fuel cell stack used as motive power source of vehicle (all claimed) such as motor vehicle and electric vehicle.    ADVANTAGE - The transition metal nitride is manufactured efficiently and economically with excellent productivity, corrosion resistance, chemical stability and electroconductivity without impairing press-formability.    DETAILED DESCRIPTION - A transition metal nitride is obtained by nitriding base material containing austenitic stainless steel containing niobium, vanadium and titanium. The transition metal nitride has layer (A) and layer (B) formed on base layer of base material. The layer (A) has laminated crystal structure of nanometer-level containing nitride having cubic crystal structure of M4N type, nitride having hexagonal crystal structure of M2-3N type, or nitride having crystal structure chosen from Cr2N hexagonal crystal structure, CrN crystal structure, crystal structure of M4N type and hexagonal crystal structure of M2-3N type, where M is iron, chromium, nickel or niobium. The layer (B) is formed from the surface of the base material as surface nitriding treatment portion of the base material along depth direction. INDEPENDENT CLAIMS are included for the following:    (1) manufacture of transition metal nitride; and    (2) manufacture of separator.    DESCRIPTION OF DRAWING(S) - The drawings show principal-portion expansion model and sectional view of separator for fuel cell.    Base material (10)    Surface portions (10a,11a)    Nitrided layers (11,11b,11c)    Base layer (12)