When operation is to be started in a state where the SOC of a high-voltage battery has dropped, an exhaust gas recirculation pump is driven by a low-voltage battery to suck in atmosphere through an air intake valve. The atmosphere is supplied to a fuel cell stack as oxygen-containing gas, while fuel gas is supplied from a fuel tank thereto, whereby power generation is performed to thereby charge the high-voltage battery. Normal power generation of the fuel cell system is performed using the high-voltage power of the charged high-voltage battery.