NOVELTY - The electrochemical device (1) has a fuel electrode (12) which forms cathode, oxygen electrode (14) which forms anode, ion exchange membrane (13) for conducting hydrogen ions in fuel electrode into oxygen electrode and a fuel source for supplying fuel to generate hydrogen ions. The fuel electrode and fuel source constitute a fuel electrode assembly in contact with each other. The ion exchange membrane is surrounded by oxygen electrode.    USE - Power generator used in power generation system (claimed).    ADVANTAGE - The usability of the electrochemical device for portable device is improved and the degree of freedom in layout of the electrochemical device is improved. The electrochemical device is easily packaged as a product. The protons are conducted without the need of provision of humidifier. The ion exchange membrane is easily formed into a solid membrane using the proton conductor, even if the proton conductor is difficult to be formed into a film. The oxygen in the air is easily supplied into the power generation system so a rechargeable power generation system is formed.    DETAILED DESCRIPTION - The electrochemical device comprises a fuel electrode which forms cathode while accompanying generation of hydrogen, and oxygen electrode provided so as to contact with oxygen and forms anode while accompanying generation of water from oxygen molecules, hydrogen ions and electrons. The device has an ion exchange membrane for conducting hydrogen ions in fuel electrode into oxygen electrode and a fuel source for supplying a fuel to generate hydrogen ions in fuel electrodes. The fuel electrode and fuel source constitute a fuel electrode assembly in contact with each other. The ion exchange membrane has a proton conductor. The fuel electrode assembly is surrounded by ion exchange membrane in contact with ion exchange membrane. The ion exchange membrane is surrounded by oxygen electrode in contact with oxygen electrode.    INDEPENDENT CLAIMS are included for the following:    (1) a power generator having several electrochemical devices; and    (2) a power generation system.    DESCRIPTION OF DRAWING(S) - The figure shows a section of the electrochemical device.    Electrochemical device (1)    Hydrogen absorber (11)    Fuel electrode (12)    Ion exchange membrane (13)    Oxygen electrode (14)