To suppress a rapid voltage change in each power generation cell constituting a fuel cell stack, power storage devices 11 are respectively connected to each power generation cell 2 or each cell assembly including a plurality of power generation cells 2 of a fuel cell stack 1 to transfer electric charges between each power generation cell 2 and the corresponding power storage device 11. This allows a voltage control to be performed for each power generation cell 2, and thus improves the durability of the fuel cell stack.