NOVELTY - An electrolytic membrane structure comprises an electrolytic membrane (1) between an anode and a cathode, a catalyst layer (2) formed by closing up conductive particles (4) carrying catalysts on each face in the anode and cathode and a boundary layer (3) adjacent to the catalyst layer in the anode on one face of the electrolytic membrane. Each face of the catalyst layer contacts each of the electrodes.    USE - For fuel cell (claimed), for generating power with fuel gas and oxidant gas.    ADVANTAGE - The boundary layer that is placed at position easily contacting the oxygen around the catalyst layer is formed of conductive particles carrying a small amount of the catalyst. Thus, even if the oxygen passes through the vicinity of the electrode and reaches the boundary layer, the oxygen is difficult to burn and react with the hydrogen rapidly, which restricts the temperature increase due to the combustion and increases the durability of the fuel cell. The hydrogen that has reached the boundary layer generates the electrochemical reaction, but since the catalyst amount in the boundary layer is smaller than the catalyst layer, the electrochemical reaction in the boundary layer is mild, and the reaction heat to be generated is smaller than in the catalyst layer. This slow electrochemical reaction reduces unreacted hydrogen gas in the vicinity of the catalyst layer including the boundary layer, thus avoiding concentration of the unreacted gases in the vicinity of the periphery of the catalyst layer. The power generation efficiency of the boundary layer is improved.    DETAILED DESCRIPTION - The boundary layer is formed between a portion to be easily contacted with an oxygen gas and the catalyst layer in the anode. The catalyst-carrying amount in the boundary layer is smaller than a catalyst-carrying amount in the catalyst layer.    DESCRIPTION OF DRAWING(S) - The figure shows the above electrolytic membrane structure.    electrolytic membrane (1)    catalyst layer (2)    boundary layer (3)    conductive particles (4)    catalyst particles (5)