In a motorcycle, a side cover (8) is mounted to a rear body (2) of a motorcycle body, an opening is formed to the side cover at a portion facing an fuel oil supply port (10) of a fuel tank (7) disposed inside the side cover and a fuel tank lid assembly including a fuel tank lid (12) is provided for covering the opening to be opened or closed. A fuel tank lid assembly of the motorcycle is characterized in that the side cover (8) has a rear portion (8b), an upper portion (8c) and a side portion (8a) continuous to the rear and upper portion through a smooth curved portion, and the fuel tank lid has a curved surface for covering the opening (11) so that an outer surface of the fuel tank lid is substantially made flash with an outer surface of the side cover at which the opening (11) is formed when the fuel tank lid is closed. The fuel tank lid (12) is provided with an engaging member disposed inside the side cover and the fuel tank lid assemby includes a fuel tank lid locking device (28) which is engaged with the engaging member of the fuel tank lid, the fuel tank lid locking device being arranged inside the side cover. The motorcycle is provided with a seat (3) which is locked by a seat lock device (41) disposed inside the rear cowling. The seat and the fuel tank lid are selectively locked and unlocked through a lock cable (40) means connecting the fuel tank lid locking device and the seat lock device.