An object of the present invention is to provide a polymer electrolyte fuel cell capable of producing a high output without causing a drop or instability of the cell voltage of the fuel cell and a generating system having the polymer electrolyte fuel cell mounted thereon.A fuel cell system, wherein if, in a polymer electrolyte fuel cell having a cell comprising separators sandwiching an electrolyte membrane and electrodes, a temperature (Tmax) at which a standard deviation of a cell voltage begins to increase when water content retained in the cell is increased under conditions under which a cell temperature, a gas entrance dew point, and a current are specified and the temperature (Tmin) at which an average value of the cell voltage begins to drop when the gas dew point is decreased under conditions under which the cell temperature, gas entrance dew point, and current are specified are defined, the water content retained in the cell satisfies: upper limit of a maximum amount of water retained in a cell≧water content retained in a cell≧lower limit of a maximum amount of water retained in a cell is provided.