A clean power supply unit with a high fuel utilization rate using a fuel cell is provided. The power supply unit of the present invention comprises a fuel cell using methanol as fuel; a secondary battery for supplying power to a load; a fuel cell control part for controlling the amount of fuel and/or air supplied to the above-mentioned fuel cell; and a power converter for converting the power output from the above-mentioned fuel cell to a predetermined voltage or current, supplying power to the load and/or the above-mentioned secondary battery and controlling the supplied power so as to fall within a predetermined range including the value at which the amount of methanol discharged from the above-mentioned fuel cell becomes minimized.