NOVELTY - Fuel cell stack (100) comprises unit cells stacked so that they sandwich a separator to form, between oxygen electrodes, an oxidizing gas chamber to which a mixed flow of air and water is supplied. The oxidizing gas chamber has an inlet port in an upper portion for the mixed flow and an outlet port in a lower portion for the mixed flow. The outlet port has a projecting portion that causes water droplets that accumulate on a wall surface of the oxidizing gas chamber to fall off.    USE - For use in a fuel cell system (1) for, e.g. electric automobile.    ADVANTAGE - The fuel cell stack improves air flow by promoting discharge of coolant water. The water that is taken in through the inlet port along with air runs down the projecting portion from the outlet port and falls off, so water droplets do not obstruct the outlet port, and air flows through without any delay. The projecting portion has a surface continuous with an inner wall surface of the oxidizing gas chamber, making it easy for water droplets to pass out of the oxidizing gas chamber and fall off. The fuel cell stack can be assembled easily.    DETAILED DESCRIPTION - Fuel cell stack comprises unit cells, each of which is made up of an electrolyte layer plus a fuel electrode and an oxygen electrode that are provided on opposite sides of the electrolyte layer. The unit cells are stacked so that they sandwich a separator to form, between the oxygen electrodes, an oxidizing gas chamber to which a mixed flow of air and water is supplied. The oxidizing gas chamber has an inlet port in an upper portion for the mixed flow and an outlet port in a lower portion for the mixed flow. The outlet port has a projecting portion that causes water droplets that accumulate on a wall surface of the oxidizing gas chamber to fall off. The projecting portion is formed by extending collector member, a partition, or oxygen electrode downward. It has a slanting portion in which a lower edge of the projecting portion is slanted. A water-repellant treatment is applied to a lower edge of the projecting portion.    DESCRIPTION OF DRAWING(S) - The figure is a block diagram that shows a fuel cell system.    Fuel cell system (1)    Fuel supply system (10)    Air supply system (12)    Water supply system (50)    Fuel cell stack (100)