NOVELTY - The separator (20) has a set of metallic plates (21, 31) that is welded with each other. The set of metallic plates is separated from each other at the beginning. A set of curved regions (61) is arranged symmetrical with regard to each other. The set of curved regions is formed around a welded region of the set of metallic plates. A surface of one of the set of metallic plates is formed as a reaction surface. The surface is provided with a channel (23) for a reaction gas. A cooling surface is provided with a cooling passage (25).    USE - Metallic separator for a fuel cell in a fuel cell stack in a fuel cell vehicle (all claimed) such as passenger car and all-wheel propelled off-road SUV. Can also be used for a bus, lorry, different commercial vehicles, watercrafts including a multitude of boats and ships, airplanes, hybrid vehicles, electric cars, plug in hybrid electric cars, hydrogen-propelled vehicles and other vehicles with alternative fuel such as fuel produced from resources with exception of petroleum, and petrol propelled vehicle.    ADVANTAGE - The set of curved regions is formed around the welded region of the set of metallic plates, thus enhancing the air tightness of the fuel cell with a simple configuration, increasing productivity, and reducing separator defects. The unyieldingness of the fuel cell is enhanced, and the deformation of the fuel cell is avoided. The surface contamination of the fuel cell is prevented, and the productivity of the entire fuel cell stack is improved. The fuel cells are able to be stacked one on the other, thus achieving external insulation of the separator, and providing uniformity regarding the length of the stack.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a fuel cell stack    (2) a fuel cell vehicle.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a configuration of a fuel cell stack.    Metallic separator (20)    Metallic plates (21, 31)    Reaction gas channel (23)    Cooling passage (25)    Curved regions (61)