an all terrain vehicle is constructed to prevent rainwater or the like from entering an inner portion of an air cleaner without complicating the structure of the vehicle or making the assembly work difficult , while improving the external appearance of the vehicle . an air cleaner is provided below a seat , and the air cleaner is positioned between left and right rail main bodies when viewed from above . left , right , bottom and rear surfaces of the air cleaner are covered with an undercover , which is separate from the air cleaner .