A fuel cell stack is provided in which a reaction gas can be uniformly distributed among fuel cell units disposed within the stack. In particular, the fuel cell stack contains a plurality of fuel cell blocks which are stacked upon each other, and each fuel cell block contains a plurality of fuel cell units which are stacked upon each other. The reaction gas is supplied to each fuel cell block via an external manifold located outside the fuel cell stack. An internal manifold is located within each fuel cell block and receives the reaction gas from the external manifold. Subsequently, the internal manifold distributes the gas to each fuel cell unit. As a result, the fuel cell stack is able to uniformly distribute the reaction gas to each fuel cell unit, thereby increasing the efficient utilization of fuel.