FUEL CELL SYSTEM

A fuel cell system (10) includes a fuel cell stack (116) and a control device (60) that controls operation of the fuel cell system (10) based on a measured voltage value measured by a voltage sensor (91). When the fuel cell system (10) is started and a value measured by a temperature sensor (38) is equal to or less than a temperature determined in advance, the control device (60) raises the voltage of the fuel cell stack (116) until a voltage condition determined in advance is met, by supplying a cathode with an oxidant gas before current sweep is started. The control device (60) sets a voltage command value and a current command value such that an operation point of the fuel cell stack (116) is on an equal power line of the fuel cell stack (116) when the operation point is caused to transition in at least a part of a transition period.