To provide a suction adapter for an engine of such a structure that a mixture gas having a high mixing efficiency prepared by mixing the air with the fuel uniformly and perfectly is sucked into a cylinder, capable of enhancing the rate of combustive consumption of the engine and its power characteristics.

The suction adapter of the engine is composed of an outer pipe 1 to be fitted on a suction pipe, a plurality of inner pipes 2 accommodated in the outer pipe 1, inscribed with its inside surface, and circumscribed with one another, and a spiral groove 20 formed at the inside surface of each inner pipe 2, whereby the air in the suction pipe is introduced into the inner pipes 2 and vortices are produced by the spiral groove 20. It is preferred that any specific one of the inner pipes 2 has a right-handed spiral groove 20, while the other inner pipes 2 have left-handed spiral grooves 20.