PURPOSE: To form the size of a carburetor in the vertical direction as short as possible so as to attain miniaturization of the carburetor by sandwiching the inner circumferential edge part of a diaphragm with a horizontal turning part and a retainer fitted to a lower hanging down part.

CONSTITUTION: A vacuum piston 5 is elevatably fitted in a guide cylinder 4, and the outer circumferential part of the top end contacting flange 5a of the vacuum piston 5 contacting with the upper end edge 4a of the guide cylinder 4 is formed downward foldedly into a cylindrical shape. Further the lower part of the cylindrical hanging down part 5b is turned perpendicularly outward so as to form a horizontal turning part 5c. The inner circumferential edge part 7a and the outer circumferential edge part 7b of a diaphragm 7 are respectively applied on the horizontal turning part 5c and the upper end flange part 6a of an outer cylinder part 6, and a retainer 8 is threadedly fitted or press- fitted to the cylindrical hanging down part 5b. Hereby, the vertical size of a carburetor 1 can be formed as short as possible, so as to attain miniaturization of the carburetor 1.