In a transmitting system for a small-sized vehicle, a centrifugal clutch, and a torque converter including a pump impeller connected to an output drum of the centrifugal clutch and a turbine impeller connected to an output gear, are placed between a crankshaft of an engine and the output gear. The pump impeller and the output drum adjacent to the pump impeller are integrally coupled, with an open surface of the output drum facing to an opposite side to the pump impeller, to be constructed as a single component. Thus, occurrence of rotation vibrations and unusual noises can be prevented without requiring machining with high precision, and the numbers of components and assembling steps can be reduced while providing favorable maintainability.