PURPOSE: To ensure the easy mounting and demounting of a muffler by spliting a motorcycle seat cowl into two portions of front and rear cowls from the rear side of a seat, fixing the front seat cowl to a body frame and so providing the rear seat cowl as free to be mounted or demounted to and from the front seat cowl.

CONSTITUTION: A rear seat cowl 21 is demounted in such a way that the front portion thereof is deflected for releasing the engaged condition of an engagement part 20, separated from a front set cowl 19 and then moved to the rear side of a body. By demounting the rear cowl 21 as aforementioned, an area under a seat 17 or the mounting positions of cushion unit 13 and a muffler 14 are exposed. As a result, maintenance work such as the adjustment of the cushion unit 13, the mounting and demounting of the muffler 14 can be carried out only by demounting the rear seat cowl 21.