To provide a starting device of a rotary throttle valve type carburetor by reducing the height from a carburetor main as small as possible and to compact the carburetor.

A start operation lever 21 forming the starting device for cold start is provided rotatably about an axis parallel to the rotary shaft of a lever member 4 integral with a rotary valve element. A protruding shaft 21a is provided on a lower surface of the start operation lever and supported on a hole 1b formed in the carburetor main body 1, and an upper surface of the start operation lever is supported by a holding member 14a integrally formed on a pump cover 14. The start operation lever is not displaced vertically in an axial direction of the rotary valve element. The height of the start operation lever does not therefore become large needlessly and is not affected even when a ratio of longitudinal lengths measured from the rotary shaft of the start operation lever as a fulcrum is increased, the starting device can be made compact and the length ratio can be increased to displace the lever member with small operation force.