Claims

1. A fuel cell stack comprising a plurality of fuel cell units stacked, each having an oxygen supply layer on a side of one surface of an electrolyte membrane,wherein each of the oxygen supply layers has an opening opened to an atmosphere in at least a part of a side surface thereof, and diffuses oxygen in the atmosphere from the opening to the side of the one surface of the electrolyte membrane, and diffuses vapor from the side of the one surface of the electrolyte membrane to the opening, andwherein ventilation performance of a gas from and to the atmosphere in each of the oxygen supply layers in all of the fuel cell units is adjusted such that an oxygen supply layer in a fuel cell unit having a higher water vapor partial pressure during operation has a higher ventilation performance of the gas than an oxygen supply layer in a fuel cell unit having a lower water vapor partial pressure during operation.