FIG. 11 is a graph showing the current-to-voltage characteristic, the current-to-power characteristic, and the release ratio characteristic for a quantity of supplied methanol (fuel) in the DMFC. Referring to FIG. 11, the ordinate is used for an output voltage (V), output power (W), and a release ratio (%) of the DMFC, and the abscissa is used for an output current (A) of the DMFC. C11 through C13