NOVELTY - Fuel cell stack comprises stacked unit fuel cells interposed and held by end plates. A gas supply passage (1, 3) and a gas discharge passage (2, 4) are formed penetrating through the stacked unit fuel cells and one of the end plates in such manner that they communicate with a reaction gas passage (51) of each unit fuel cell. A drainage passage (8A, 8B) is formed penetrating through the stacked unit fuel cells and one of the end plates. An end of the drainage passage and an end of the gas discharge passage on the side of the other end plate are joined to each other.    USE - For use in vehicle.    ADVANTAGE - The size of fuel cell stack is reduced because the ends of gas discharge passage and drainage passage can be joined to each other without using external piping, thus reducing the manufacturing cost and the occupied space.    DETAILED DESCRIPTION - Fuel cell stack comprises stacked unit fuel cells and end plates for interposing and holding the stacked unit fuel cells from both sides along a direction in which the unit fuel cells are stacked. Each unit fuel cell includes a membrane electrode assembly (20) comprising an electrolyte membrane interposed between an anode and a cathode. A pair of separators (30A, 30B) respectively closely contacts the anode and cathode to respectively form reaction gas passages between one of the separators and the anode, and between the other separator and the cathode. With respect to each of the reaction gas passage facing toward the anode and the reaction gas passage facing toward the cathode, a gas supply passage and a gas discharge passage are formed penetrating through the stacked unit fuel cells and one of the end plates in such manner that they communicate with the reaction gas passage of each unit fuel cell. A drainage passage is formed penetrating through the stacked unit fuel cells and one of the end plates. An end of the drainage passage and an end of the gas discharge passage on the side of the other end plate are joined to each other.    DESCRIPTION OF DRAWING(S) - The figure shows an exploded view of a unit fuel cell.    Gas supply passage (1,3)    Gas discharge passage (2,4)    Drainage passage (8A,8B)    Membrane electrode assembly (20)    Separators (30A,30B)    Reaction gas passage (51)