In a fuel cell system which includes a high-electricity multiple-phase converter, noise generated due to an increase in reactor vibrations and due to a sound pressure increase caused by a plurality of reactors is effectively inhibited, and silence is improved. A fuel cell system includes a multiple-phase converter provided between a fuel cell and a load device. The fuel cell system includes: selecting means (e.g., a controller) for selecting a driving phase of the multiple-phase converter in accordance with the load of the load device; and driving means (e.g., a controller) for driving a plurality of driving phases, when selected by the selecting means, at carrier frequencies so that these driving phases are nearly opposite to each other.