A fuel cell system includes an ion-exchange filter, which is provided with a cartridge which is filled up with an ion-exchange resin. The cartridge includes one of a pressure-loss emphasizing type cartridge and an ion-exchange efficiency emphasizing type cartridge, which are selectively exchanged with each other, for a common case of the ion-exchange filter. The ion-exchange efficiency emphasizing type cartridge is one for an ion-exchange filter having a high pressure loss and high ion-exchange efficiency and, on the other hand, the pressure-loss emphasizing type cartridge is one for an ion-exchange filter having a pressure loss lower than that of the former ion-exchange filter and an ion-exchange efficiency lower than that of the former ion-exchange filter.