A fuel cell system includes a fuel cell system connector and a fuel cartridge connector. The fuel cell system connector includes an external structure configured to accommodate a connector of a fuel cartridge and an internal structure mounted in the external structure. A contacting surface between the external structure and the internal structure of the fuel cell system connector includes a first nano-processed surface on a fuel supply path. The fuel cartridge connector includes an external structure having a retention key and an internal structure mounted in the external structure. A contacting surface between the external structure and the internal structure of the fuel cartridge connector includes a second nano-processed surface on a fuel supply path.