A fuel cell system that includes: an ion exchanger that is provided at a circulation path and that restores insulation resistance of a coolant; a detector that is provided at the circulation path at a downstream side of a radiator in a circulation direction of the coolant and that detects conductivity of the coolant; and a controller that is electrically connected to the detector and a pump and that controls driving of at least the pump. In a state in which the pump is stopped and in a case in which the insulation resistance of the coolant, which is obtained from the conductivity of the coolant that has been detected by the detector, becomes equal to or less than a specific value, the controller starts the driving of the pump such that the coolant passes through the ion exchanger.