A fuel cell generally has a stack structure including a plurality of stacked unit cells. Each unit cell has a structure where a membrane electrode assembly and a separator are disposed to face each other and a gas flow path is disposed between the membrane electrode assembly and the separator. The gas flow path is used for supplying reactive gas along a surface of the membrane electrode assembly. For example, the gas flow path is formed in a manner such that the reactive gas flows from a supply hole for the reactive gas provided in an outer edge portion of the separator, passes along the entire surface of the membrane electrode assembly, and travels toward a discharge hole provided in another outer edge portion opposite to the outer edge portion where the supply hole is provided. For example, patent literature 1 teaches a separator including gas passage grooves and a communication groove interconnecting adjacent portions of the gas passage grooves. The communication groove is shallower than the gas passage grooves.