Abstract: A drive system for an engine-driven light vehicle which transmits the engine rotation to a wheel of the vehicle through a friction roller during normal engine operation, and transmits the wheel rotation to the engine through the friction roller to start the engine. The friction roller has its drive shaft disposed parallel with the crankshaft of the engine, between which shafts is interposed a power transmission means, e.g. a gear train meshing with each other. At least one gear of the gear train is rotatably fitted on the crankshaft, with which engages a one-way clutch for transmitting the drive shaft rotation to the crankshaft with a ratio of speed change preset for the start of the engine. A planetary gear is coupled to the gear train for transmitting the crankshaft rotation to the drive shaft through the gear train with a large reduction ratio.