A silencer installed in a fuel cell system includes a plurality of expansion chambers connected to a predetermined apparatus of the fuel cell system, wherein the plurality of expansion chambers serially reduces acoustic noise of air discharged from the predetermined apparatus and a resonator connected to an expansion chamber of the plurality of expansion chambers, wherein the resonator reduces acoustic noise received from the expansion chamber in another frequency band, which is different from a frequency band of the acoustic noise reduced by the plurality of expansion chambers, where one of the plurality of expansion chambers comprises an inlet pipe which receives air from the predetermined apparatus, another of the plurality of expansion chambers comprises an outlet pipe which discharges air flowed into the plurality of expansion chambers, and an intermediate pipe is disposed between the plurality of expansion chambers.