A combustion engine mounted on a motorcycle includes an engine rotary shaft extending in a vehicle widthwise direction and a supercharger disposed rearwardly of a cylinder block. The combustion engine also includes an air intake duct through which an incoming wind flowing forwardly of a traveling direction with respect to the combustion engine is introduced into the supercharger. The air intake duct is fluid connected with an air intake port of the supercharger after having passed laterally of the combustion engine.