FUEL CELL SYSTEM

A fuel cell (100) includes an electrolyte membrane (120), an anode (122) which is disposed on one surface of the electrolyte membrane (120) and includes an anode catalyst layer, a cathode (124) which is disposed on the other surface of the electrolyte membrane (120) and includes a cathode catalyst layer, and an adjustment unit which allows at least one of a relative humidity of a gas which is in contact with the anode catalyst layer and a relative humidity of a gas which is in contact with the cathode catalyst layer to be decreased down to less than 100% before a fuel is supplied at the time of starting.