PURPOSE: To provide a fuel system of the private power generating facilitates for emergency which can automatically and equally select a main oil storage tank.

CONSTITUTION: For two main oil storage tanks 1A and 1B, one small-quantity fuel feed tank 2 is provided, and an oil feed system which has an oil feed pump 5 and oil feed solenoid valves 7A and 8A and a return oil system which has a return oil pump 6 and return oil solenoid valves 7B and 8B are conducted piping. Oil amount detectors 11A and 11B which detect oil levels continuously and outputs them as corresponding electric signals are installed in the main oil storage tanks 1A and 1B. A deviation decision unit 12 which detects the deviation between the output signals of both the oil amount detectors 11A and 11B is provided, and it is decided whether the amount of oil is large or small judging from the deviation detection value, thereby controlling the solenoid valves 7A and 7B, and 8A and 8B so that large one is selected.