PURPOSE: To lower the combustion temperature and enhance the fuel economics by providing two sets of power valves and additional fuel passages, and by constituting the device in such a way that additional fuel can be supplied, at places other than a main nozzle, in an engine speed in the entire region of high-load operation and in the region of at least intermediate speed operation respectively.

CONSTITUTION: In a high-load operation region in which the negative pressure in an intake pipe is low, two power valves 11, 12 are simultaneously opened, and an additional fuel measured by the valve port 14 of a first power valve 11 is aspirated into an intake passage 2 through an additional fuel passage 38 due to the negative pressure of a venturi. In the low-speed operation, since the negative pressure in the intake pipe is extremely low, a diaphragm 21 is greatly displaced towards the outlet chamber 20 to increase the opening of the power valve 11, however, since the negative pressure of the venturi is very low, the amount of aspiration to the intake passage 2 is not increased. When the engine speed enters a region greater than the intermediate- speed operation, since the intake air flow quantity increases and the negative pressure of the venturi becomes high, an additional fuel measured by the valve port 24 of a second power valve 21 is aspirated into the intake passage 2 through an additional fuel passage 39.