To improve the durability and the sealing performance in a carburetor joint 3 of a composite structure in which a cylindrical member 5 made of rubber is adhered to an annular member 4 made of resin.

The annular member 4 has an attaching piece 41 in a peripheral determined position, A reinforcement rib 47 is installed in the circumference of an air hole 42 and the attaching piece 41 in an inner end face (an end face at the carburetor 2 side) 46 of the annular member 4. Thereby, since the strength in the annular member 4 is improved, the molding precision in the annular member 4 is improved. The deflection is suppressed and prevented when attaching the attaching piece 41 to a suction part 1 of an engine with a screw 8, etc.