An air cleaner includes an upper casing, which has an inlet, a lower casing, which has an outlet and covers the lower opening of the upper casing, and a filter element, which is located inside the upper casing and the lower casing. The lower casing includes a looped application surface, on which an adhesive is applied to adhere the filter element, and a minute protrusion, which extends along the perimeter, is formed on the inner peripheral edge of the application surface.