In a fuel cell composed of a pair of separators with a membrane electrode assembly sandwiched therebetween, gas passages having a plurality of generally linear passage portions, and bent passage portions each of which makes one end portion of the linear passage portions communicated with the other end portion of the linear passage portions, are formed so as to be communicative from a gas introducing port to a discharge port. In inner wall surfaces of the groove portions of the separators constituting the linear passage portions, water-retaining groove portions capable of retaining inside thereof at least part of water generated in the gas passage are formed in such a grooved configuration as to be substantially continuous along the passage portion. As a water drop generated within the gas passage makes contact with retained water within the water-retaining groove portions, growth of the water drop is suppressed to avoid any blockage of the gas passage, by which the anti-flooding property is improved.