PURPOSE: To supply fuel to a fuel/gas chamber at a variable flow rate by providing a means for plotting an orifice for guiding fuel in a pressure fuel source and a housing, a means for opening/closing the housing in a combustion chamber and a means for adjusting an orifice dimension.

CONSTITUTION: A fuel supply system 30 is provided with a housing 32 supported by an engine block, and this housing 32 having a chamber 35 plots a fuel/gas passageway 34 having an axis 36. The housing 32 has an upper portion 38 partially plotting the passageway 34 and the upper end of the same, and having a hole 40 therein to communicate with the chamber 35. The fuel supply system 30 is provided with a valve member 80 having a piston 82 extended in the hole 40, and thus an orifice is plotted between the piston 82 and a sleeve 42. A means for adjusting an orifice dimension, or for adjusting a fuel speed passing through the piston 82 is provided.