An air cleaner case of an air cleaner used in an engine provides a lower casing holding a cleaner element thereon, and a cover accommodating the cleaner element therein. The lower casing includes a base on which the cleaner element is mounted, an exhaust duct extending downward from the base so that air purified by the cleaner element is conveyed to the intake side of the engine, an inlet duct extending downward from the base along the exhaust duct, and an inlet cylinder extending upward into the accommodating chamber from the base so as to be continuous with the inlet duct.