To lower the center of gravity of the entire engine including a speed-change actuator for realization of the lowered center of gravity of a vehicle in which the engine is mounted and to suppress the effect on an arrangement space for components above the engine. In an engine including a transmission which is provided in a power transmission pathway to a drive wheel, a counter shaft which is an output shaft of the transmission, an engine case in which a crankshaft and the transmission are accommodated, and a speed-change actuator which is attached to the engine case, the speed-change actuator is arranged below relative to the counter shaft.