A fuel cell device has a small and compact structure as a whole. The fuel cell device employs a fuel cell (e.g., direct methanol fuel cell of an MEA structure) using liquid fuel. Diluted liquid fuel is prepared by diluting the liquid fuel (methanol-contained liquid in the case of DMFC) with dilution liquid, and is supplied to the fuel cell. A first pump unit stacked on the fuel cell supplies the diluted liquid fuel to the fuel cell while diluting the liquid fuel by mixing the liquid fuel and the dilution liquid together. A second pump unit stacked on the fuel cell collects liquid (water usable as dilution liquid in DMFC) produced by an electrochemical reaction in the fuel cell.