To provide a fuel cell system capable of suppressing excessive increase in open-circuit voltage of a fuel cell.SOLUTION: A fuel cell system 1 comprises: a fuel cell 4; an air compressor 14 that supplies an oxidant gas; a valve mechanism (a bypass valve 15 and a pressure regulating valve 17) that can switch a state between a supply state where the oxidant gas is supplied to the fuel cell and a bypass state where the oxidant gas passes through a bypass pipe 13 without being supplied to the fuel cell; and a control device 3 that controls the fuel cell system. The control device has: a voltage acquisition part that acquires an open-circuit voltage which is a voltage of the fuel cell in a power generation suspending state; an intermittent operation execution part that, in a case where there is no power output request to the fuel cell, controls the fuel cell to the power generation suspending state, provides the supply state by the valve mechanism, and intermittently drives the air compressor to keep the open-circuit voltage a target voltage; and a reduction processing execution part that controls the state to the bypass state by the valve mechanism in the power generation suspending state, and stops the driving of the air compressor to facilitate reduction in the open-circuit voltage.SELECTED DRAWING: Figure 1