A fuel-cell single cell has a membrane electrode assembly sandwiched between a pair of separators, and a sealing member that seals a gas channel formed between the membrane electrode assembly and the separators. An uneven portion is formed in a part of the membrane electrode assembly where the sealing member is disposed. A sealing member sump to trap the sealing member is provided at a side exposed to reactant gas pressure and a holder part for the sealing member are provided within a part of the separators where the sealing member is disposed. The uneven portion is opposed to the holder part.