To provide a rotary throttle valve type carburetor wherein an intake negative pressure applied to a fuel injection hole of a fuel supply pipe facing a throttle hole of a rotary throttle valve is reduced when an engine speed is reduced.

In this carburetor, a wall part of a carburetor body 2 is formed with passages 9, 10 connecting an inlet 7a and an outlet 7b of an intake path 7, and the passages 9. 10 are disposed with a check valve 12 allowing a flow of intake air to the outlet 7b from the inlet 7a.