In a fuel cell system, regeneration-time voltage fixed control is implemented where during regeneration or when regeneration is expected to occur, output voltage of a fuel cell is set to a voltage value outside an oxidation reduction progress voltage range, and the amount of reactant gas supplied to the fuel cell is changed based on the amount of electric power remaining in an energy storage device. In the regeneration-time voltage fixed control, it is determined whether or not regeneration occurs while a moving body equipped with the fuel cell system is moving down a slope, and in the case where it is determined that regeneration occurs while the moving body is moving down a slope, the amount of the reactant gas supplied to the fuel cell is decreased in comparison with the case where it is determined that regeneration occurs while the moving body is not moving down a slope.