The present application provides a technique prevents a regulator arranged on a gas supplying path that supplies gas to a fuel cell installed in a fuel cell system from functioning erroneously, by controlling the pressure increase within the upper stream side of the regulator. The fuel cell system includes a fuel cell, an oxide gas supplying path to supply oxide gas to the fuel cell, a fuel gas supplying path to supply fuel gas to the fuel cell, a secondary regulator arranged on the fuel supplying path, a bypass path communicating the upper stream side path of the secondary regulator with the lower stream side path of the secondary regulator, and a pressure controlling valve that is closed in a case where the pressure difference between the upper stream side path and the lower stream side path is less than a predetermined amount, and opened in a case where the pressure difference between the upper stream side path and the lower stream side path exceeds the predetermined amount.