Miniaturization is achieved when a membrane-electrode assembly (MEA) is provided with a cutout, and the flow of a fluid is further smoothened. To realize this, in a separator for a fuel cell according to the present invention, a portion of the contour of a manifold formed in the separator corresponding to a cutout of the membrane-electrode assembly is formed into a shape along the cutout, and a reactant gas or a coolant is supplied or discharged through a portion formed into the shape along the cutout. The cutout is, for example, a corner cut provided in the corner of the membrane-electrode assembly and forming the membrane-electrode assembly into an asymmetric shape. A portion of the contour of the manifold facing this corner cut is preferably formed substantially in parallel with the edge of the corner cut.