To suitably keep the weight balance of an engine while reducing a radial dimension of the engine. A crank shaft and a transmission shaft are supported in casings and are disposed to be substantially parallel to each other. A rear balancer and a front balancer are disposed with the crank shaft placed therebetween. An AC generator is disposed at an end portion of the crank shaft on the left side with respect to a plane passing through a center of gravity of an engine and being perpendicular to the crank shaft. A clutch is disposed at an end portion of the transmission shaft on the right side with respect to the plane. The clutch is separated from the plane at a distance smaller than that between the AC generator and the plane, so that the weight balance of the engine is suitably maintained by disposing the rear balancer and the front balancer on the clutch side.