A fuel cell (1) includes a stacked body of a membrane electrode assembly (3) and of separators (2). Then, the membrane electrode assembly (3) and the separators (2) are formed into a substantially rectangular shape, the separators (2) include flow passages. Moreover, an aspect ratio R as a ratio (flow passage length/flow passage width) of a flow passage length with respect to a flow passage width is 0.01 or more to less than 2. Furthermore, a horizontal direction equivalent diameter D (mm) of the flow passages satisfies Expression (1): D=B×(R×Acat)1/3  Expression (1) where Acat is a catalyst area (cm2) of the membrane electrode assembly (3), and B is a constant of 0.005 or more to 0.2 or less.