In a motorcycle, the frame body has the shape of a single pipe over its whole length, and carries a front shield at its front portion, a floor at its intermediate portion, and a body cover at its rear portion, respectively. The front shield is formed of a one-piece member formed integrally with a head lamp housing, an auxiliary fender, leg shields, and foot rests. The body cover is formed of a one-piece member formed integrally with a plurality of continuous vertical walls which cooperatively enclose a space below the seat. The floor is joined at its opposite lateral edges to a pair of brackets mounted on the intermediate portion of the frame body at opposite lateral sides of the latter.