NOVELTY - A water vapor electrolyzer (1) comprises electrolytic cell (3) and unit for introducing water vapor into the cell. The cell consists of cathode interposed between fluorine resin-based ion exchange membrane (4) and fluorine resin-based ion exchange membrane (5) having catalyst, anode provided in the outer side of membrane (5) and water vapor introduction phase provided on outer side of membrane (4).    USE - Used for supplying oxygen in aircraft and jewelry processing burner, and for supplying oxygen and hydrogen to fuel cell.    ADVANTAGE - The water vapor electrolyzer enables to produce oxygen and hydrogen with high purity. The electrolyzer is compact and lightweight. The installation of vapor-liquid separation tank, water vapor cooling unit and purification unit is eliminated.    DETAILED DESCRIPTION - A water vapor electrolyzer (1) comprises electrolytic cell (3) and unit for introducing water vapor into the cell. The cell consists of cathode (7) interposed between fluorine resin-based ion exchange membrane (4) and fluorine resin-based ion exchange membrane (5) having catalyst and anode (9) provided in the outer side of ion exchange membrane (5). Water vapor introduction phase is provided on the outer side of ion exchange membrane (4). Water vapor introduced in the phase passes through the membrane (4) and cathode. The membrane (5) absorbs water and is electrolyzed by the voltage applied on the electrodes. Proton moves inside the membrane (5) from the anode to the cathode. Hydrogen is produced in the cathode surface and oxygen is produced in the anode surface without mixing with water.    DESCRIPTION OF DRAWING(S) - The figure shows the block diagram of water vapor electrolyzer. (Drawing includes non-English language text).    water vapor electrolyzer (1)    water vapor inflow port (2)    compartments (A,B,C) (3,8,11)    fluorine resin-based ion exchange membrane (4,5)    hydrogen discharge port (6)    cathode (7)    anode (9)    oxygen discharge port (10)    electrolytic cell (12)    water vapor generator (18)    pressure regulation unit (19)    safety valve (22)    temperature control unit (23)