To provide an accelerating pump of a float type carburetor in which one combined check valve is composed of an inlet valve and an exhaust valve of the accelerating pump to reduce the number of part items and assembly monhours.

A plunger 13 is fitted in a cylinder 14 formed a wall part of a fuel storage tank 2 then the accelerating pump 40 is composed. A fuel passage 9 connecting from the fuel storage tank 2 to the bottom of the cylinder 14 is provided. A passage 16 connecting from a small diameter cylindrical part 37 joined to the lower part of the cylinder 14 to an accelerating fuel nozzle is provided. A horn part 31 which is the upper half part of the combined check valve 30 composed of rubber or the like, is inserted into the cylinder 14. A flange 32 fitted to a middle part of the combined check valve 30 is attached to a stage part 36 formed by the cylinder 14 and the small diameter cylindrical part 37, a lower part conic portion 33 having a notch 34 of the combined check valve 30 juts to the small diameter cylindrical part 37.