An assembling operation of a fuel cell is effectively simplified. With the simple and economical structure, the desired sealing function is achieved. The fuel cell (10) includes a membrane electrode assembly (14) and first and second metal separators (16, 18) sandwiching the membrane electrode assembly (14). Connection channels (28a, 28b) are provided on the first metal separator (16). The connection channels (28a, 28b) connect the oxygen-containing gas supply passage (20a) and the oxygen-containing gas discharge passage (20b) to the oxygen-containing gas flow field (26). The membrane electrode assembly (14) has first overlapping portions (66a, 66b) overlapped on the connection channels (28a, 28b) for sealing the connection channels (28a, 28b). The first overlapping portions (66a, 66b) comprise, in effect, a gas diffusion layer.