In an engine, an air cleaner and a muffler are located laterally opposite to each other with an engine body therebetween, the air cleaner and the muffler are located forward of the engine body in the longitudinal direction, a fuel tank is longer laterally than longitudinally when viewed from above and is located rearward of the engine body in the longitudinal direction, and an oil filler port which is sealed by a cap is provided to the fuel tank at a position laterally deviated leftward. A level gauge, which can be visually recognized when the cap is removed and the oil filler port is viewed from above and from the front side longitudinally, is provided inside the fuel tank.