A gas flow passage formation plate includes a plurality of projections arranged in a first direction and a second direction. The projections project toward a membrane electrode assembly. The gas flow passage formation plate further includes a gas flow passage, a water flow passage, and a plurality of openings. The gas flow passage is formed by a portion of the gas flow passage formation plate at a side opposing the membrane electrode assembly including regions between two adjacent projections. The water flow passage is formed by a portion of the gas flow passage formation plate at a side opposing a partition plate including the inside of the projections. The openings are each formed in a side wall of the projection connecting inside and outside of the projection. Each opening is arranged at only one location in one projection.