To reduce the change in head difference of an oil level at the time of inclining, and operate an engine smoothly in the inclining condition by arranging a return passage between a main jet boss and an intake passage.

A main jet boss 16 is suspended to an intake passage side opposite to a return pipe 20, and a return passage 19 is arranged between an intake passage 2 and the main jet boss 16. In a circulating system carburetor, a fuel oil level is inclined around the return pipe 20, the fuel oil level is inclined between the injection port 8 of a main nozzle 7 and the main jet boss 16, and thereby, the fluctuation of head differences HL, HR at the time of inclining is set to a low level in relation to a head difference H of a normally erecting condition. It is thus possible to suppress the fluctuation of a fuel feed rate in a low level, and it is also possible to operate an engine smoothly.