NOVELTY - Fuel cell has a portion of the fuel gas flow passage, that is located near a fuel gas inlet, arranged close to a portion of the oxygen-containing gas flow passage that is located near an oxygen-containing gas outlet with an ion exchange membrane of 20 - 60 microns thickness between the gas passages.    USE - None given.    ADVANTAGE - It is possible to easily and smoothly supply water which is produced in the oxygen-containing gas flow passage to the fuel gas flow passage. Thus non-humidifying operation is performed for the fuel cell. Initial humidification is performed in a short period of time. Gas humidifying device is small in size and economical.    DETAILED DESCRIPTION - Fuel cell comprises:    (a) a fuel cell unit (12) consisting of a solid polymer ion exchange membrane (18) between an anode (22) and a cathode (20);    (b) separators (14, 16) for supporting the fuel cell unit between them;    (c) a fuel gas flow passage, for supplying, in a non-humidifying manner, a fuel gas from one side of the ion exchange membrane to the anode; and    (d) an oxygen-containing gas flow passage (42, 46) for supplying, in a non-humidifying manner, an oxygen-containing gas from the opposite side of the ion exchange membrane to the cathode.    The ion exchange membrane has a thickness of 20 - 60 microns. A portion of the fuel gas flow passage, which is located near a fuel gas inlet (36a), is arranged close to a portion of the oxygen-containing gas flow passage located near an oxygen-containing gas outlet (38b) with the ion exchange membrane between the gas passages.    An INDEPENDENT CLAIM is also included for a method of operating a fuel cell comprising: humidifying at least one of the fuel gas and the oxygen-containing gas to supply the gas for a predetermined period of time; and supplying the fuel gas without humidification to the anode and supplying the oxygen-containing gas without humidification to the cathode after a predetermined period of time.    DESCRIPTION OF DRAWING(S) - The diagram illustrates an exploded perspective view of the principal parts of a fuel cell stack.    Fuel cell stack (10)    Fuel cell unit (12)    Separators (14, 16)    Ion exchange membrane (18)    Cathode (20)    Anode (22)    Fuel gas inlet (36a)    Fuel gas outlet (36b)    Oxygen-containing gas inlet (38a)    Oxygen-containing gas outlet (38b)    Cooling medium inlet (40a)    Cooling medium outlet (40b)    Oxygen containing gas flow passage (42, 46)