The fuel cell system includes: a fuel cell unit including first and second fuel cells connected to each other in parallel; a supply system that supplies a reactant gas to the fuel cell unit; a required output power obtainment unit configured to obtain required output power to the fuel cell unit; a supply system control unit configured to control the supply system such that output power of the fuel cell unit is the required output power; a determination unit configured to determine whether or not a predetermined condition is satisfied; and a performance obtainment unit configured to obtain output power performance of the first fuel cell.