It is an object of the present invention to provide a high efficiency hybrid power supply system that permits a power type power supply device such as a capacitor to be utilized effectively, and that makes it possible to even the burden on an energy type power supply device such as a storage cell. A capacitor 21 is connected to system voltage lines 26 and 27 which are connected to a load 30, and a body formed by a serial connection between a large-capacity storage cell 22 and the output terminal of a voltage controller 23 is connected in parallel with this capacitor 21. The voltage Vb of the storage cell 22 is substantially constant. The voltage controller 23 is a DC/DC converter, for example, the output voltage Vv of which is variable. A system controller 25 changes the system voltage Vs by changing the output voltage Vv of the voltage controller 23. When a large amount of electric power is to be supplied to the load 30, energy is rapidly discharged from the capacitor 21 and supplied to the load 30 by lowering the system voltage Vs. When a large amount of electric power is to be fed back from the load 30, energy from the load 30 is rapidly absorbed by the capacitor 21 by raising the system voltage Vs.