NOVELTY - The apparatus (1) has a fuel cell (2) e.g. active direct methanol fuel cell (DMFC), and a secondary battery (4) e.g. lithium-ion battery, for storing electric power in response to a fluctuation in a load current. Connection terminals (7, 8) connect a load apparatus e.g. cell phone. A direct current-direct current (DC-DC) converter converts an output voltage of the cell into a charging voltage for charging the battery. Another direct current-direct current (DC-DC) converter converts an output voltage of the battery into a set output voltage that is delivered to the terminals.    USE - Used in a mobile body such as hybrid electric car, electric car, electric motorbike and electrical-assist bicycle, for supplying electric power to a load apparatus e.g. portable electronic equipment such as portable personal computer, cell phone, portable music reproducer and portable game machine, motive-power circuit and control circuit of the mobile body, and electric machine such as electrically-driven tool, and as a stationary charging apparatus for charging a secondary battery e.g. lithium-ion battery and nickel-hydrogen battery, that is used as a power source of the portable electronic equipment or the mobile body and an emergency power-supply source or an outdoor gear.    ADVANTAGE - The direct current-direct current (DC-DC) converter converts the output voltage of the secondary battery into the set output voltage that is delivered to the connection terminals, so that the power obtained by the fuel cell is supplied to the load apparatus, thus supplying the power for a long-time to the load apparatus, and setting the set output voltage without any restrictions from the secondary battery output voltage, and hence enhancing the degree of freedom to set the output voltage, and making the power supply apparatus to be used as a power source for the load apparatus. The secondary battery stores the electric power in response to the fluctuation in the load current, thus improving the output-voltage stability. The apparatus regulates the fuel cell`s output voltage, so that the fuel cell has the maximum power-generation efficiency, thus improving the fuel cell`s power-generation efficiency. The apparatus sets a quantity of fuel supplied to the fuel cell, so that the secondary battery`s charging-and-discharging current is reduced, thus adjusting the electric power taken out for a long time from the fuel cell, and hence continuously narrowing the width of fluctuations in the charging-and-discharging power of the battery, and reducing the capacity of the battery to make the battery smaller.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram illustrating a configuration of a power supply apparatus.    Power supply apparatus (1)    Fuel cells (2, 21)    Secondary battery (4)    Connection terminals (7, 8)