A fuel cell system comprising: a plurality of fuel cell stacks (1A, 1B, 1C) that generate electric power using a hydrogen-containing gas and an oxidant gas; a plurality of power controllers (2A, 2B, 2C) that are respectively connected to the plurality of fuel cell stacks (1A, 1B, 1C) and that extract electric power generated by the plurality of fuel cell stacks (1A, 1B, 1C), wherein only one of the plurality of power controllers (2A, 2B, 2C) is set as a master power controller, while the one or more power controllers other than the master power controller are each set as a slave power controller, the master power controller is capable of grid-independent operation during power grid failure; and characterized by a control device that controls the operation of the plurality of fuel cell stacks (1A, 1B, 1C) and the operation of the plurality of power controllers (2A, 2B, 2C) so that the number of at least either the fuel cell stacks in operation or the power controllers in operation is varied as a function of a load to be driven, wherein the fuel cell system is configured so that: (i) the master power controller is set by the control device so that the operating time of the one or more fuel cell stacks connected to the one or more slave power controllers is longer than the operating time of the fuel cell stack connected to the master power controller; or (ii) the fuel cell system further comprises voltage measurement units (4A, 4B, 4C) that measure the respective voltages of the plurality of fuel cell stacks (1A, 1B, 1C), and when the voltage of the fuel cell stack connected to the power controller acting as the master power controller is below a predetermined value, one of the plurality of power controllers other than the power controller having acted as the master power controller is newly set as the master power controller by the control device. a plurality of fuel cell stacks (1A, 1B, 1C) that generate electric power using a hydrogen-containing gas and an oxidant gas; a plurality of power controllers (2A, 2B, 2C) that are respectively connected to the plurality of fuel cell stacks (1A, 1B, 1C) and that extract electric power generated by the plurality of fuel cell stacks (1A, 1B, 1C), wherein only one of the plurality of power controllers (2A, 2B, 2C) is set as a master power controller, while the one or more power controllers other than the master power controller are each set as a slave power controller, the master power controller is capable of grid-independent operation during power grid failure; and characterized by a control device that controls the operation of the plurality of fuel cell stacks (1A, 1B, 1C) and the operation of the plurality of power controllers (2A, 2B, 2C) so that the number of at least either the fuel cell stacks in operation or the power controllers in operation is varied as a function of a load to be driven, wherein the fuel cell system is configured so that: (i) the master power controller is set by the control device so that the operating time of the one or more fuel cell stacks connected to the one or more slave power controllers is longer than the operating time of the fuel cell stack connected to the master power controller; or (ii) the fuel cell system further comprises voltage measurement units (4A, 4B, 4C) that measure the respective voltages of the plurality of fuel cell stacks (1A, 1B, 1C), and when the voltage of the fuel cell stack connected to the power controller acting as the master power controller is below a predetermined value, one of the plurality of power controllers other than the power controller having acted as the master power controller is newly set as the master power controller by the control device. (i) the master power controller is set by the control device so that the operating time of the one or more fuel cell stacks connected to the one or more slave power controllers is longer than the operating time of the fuel cell stack connected to the master power controller; or (ii) the fuel cell system further comprises voltage measurement units (4A, 4B, 4C) that measure the respective voltages of the plurality of fuel cell stacks (1A, 1B, 1C), and when the voltage of the fuel cell stack connected to the power controller acting as the master power controller is below a predetermined value, one of the plurality of power controllers other than the power controller having acted as the master power controller is newly set as the master power controller by the control device.