PURPOSE: To prevent the wear of flow controlling valve and as well as improve the responsiveness of flow rate control by a method wherein branch pipes with different inside diameters are selectively used and as well as the flow rate is controlled by changing the temperature of liquid fuel in the branch pipes.

CONSTITUTION: A distributing pipe 5 for liquid fuel is provided with a plurality of numbers of the branch pipes 6A, 6B and 6C, which have different inside diameters from one another. The flow controlling valves 7A, 7B and 7C are respectively provided in the branch pipes 6A, 6B and 6C. The branch pipe, the wear and/or blockade of the flow rate controlling valve provided in which does not occur, is selectively used. Furthermore, the flow rate is controlled by changing the opening degree of the flow controlling valve 7A, 7B or 7C of the selected branch pipe and as well as by changing the temperature of the mixed fuel in the pipe by means of a temperature controller 8.