PURPOSE: To prevent over-rich stall caused by the icing of a slow air bleed.

CONSTITUTION: The air intake of a first alow air bleed passage 6 is open at a large venturi part 4. A first slow air bleed 8A has a cylindrical shape as a whole and is formed in a manner that its head part 8d having a jet 8a protrudes into the slow air bleed 6 toward the downstream of the slow air bleed 6. A second slow air bleed 10 is provided in a second slow air bleed passage 9 and air from the slow air bleed 10 flows toward the head part 8d of the first slow air bleed 8A.