The lower end of a filler tube is attached to a service hole formed on a cylinder block in a horizontally opposed engine on a rear side of the engine, e.g., on side opposite from which an output shaft projects. The filler tube is provided with an elbow at the lower end thereof, and the elbow is integrally formed with a hole cover. When one end of the elbow is inserted into the service hole and the hole cover is fixed to the cylinder block, the connection of the filler tube and closing of the service hole can be simultaneously accomplished. The filler tube extends upward and a cap is attached on the filler port at the upper end facing toward the vicinity of the lid provided on the cowl 20. The lid 21 is not deformed locally, and forms a curved surface continuing from remaining portion of the cowl 20.