A fuel gas flow field is formed on a surface of a rectangular first metal separator. The fuel gas flow field includes flow grooves extending in the direction of gravity. An outlet buffer is provided at a lower end of the fuel gas flow field. The outlet buffer includes an inclined surface inclined toward a fuel gas discharge passage. The fuel gas discharge passage is positioned below the outlet buffer. Outlet channel grooves are formed by ridges provided between the fuel gas discharge passage and the outlet buffer. Lower ends of the ridges are arranged in a zigzag pattern.