A fuel cell stack for generating electrical energy by an electrochemical reaction of a fuel and an oxidizing gas including a plurality of electricity generating units and a fastening member is disclosed. The plurality of electricity generating units are configured for an electrochemical reaction between the fuel and the oxidizing gas to generate electrical energy, and the fastening member combines the plurality of electricity generating units into a stack. Each electricity-generating unit includes a membrane electrode assembly (MEA) and separators that are provided on each side of the MEA. Each separator comprises a channel on a surface facing the MEA. The channel is divided into a multiple of 2 sub-channels that is greater than 2 on a surface of the separator, and the sub-channels have substantially the same fluid passage length.