An air cleaner (36) mounted on a motorcycle and cleaning engine intake air (A) is provided with a lower case (50) which constitutes the cleaner body, a cover (51) which covers the upper part of the lower case (50), an element (55) which is disposed within the lower case (50) at a position below the mating surface (53) between the lower case (50) and the cover (51), and a partition wall (57) which is formed on the lower case (50), supports the element (55), and forms a part of a wall of a clean chamber (58).