To provide an air fuel ratio controller of a carburetor which can surely open or close a second bleed air passage in response to an opening of a throttle valve with a simple structure.

The air fuel ratio controller of the carburetor includes an air bleed chamber 13 formed on an outer periphery of a main nozzle 5 to communicate with an interior of the nozzle 5 via many bleed holes 14. A first bleed air passage 15 of a normal time flowing state and a second bleed air passage 16 opened or closed by control valves 20 are connected to the chamber 13. In the controller, the valves 20 are constituted of a part of throttle valves 7 so as to open or close the passage 16 in response to the opening of the valves 7.