PURPOSE: To simplify the structure of control system by arranging plural unit electric motors around an output shaft, and changing combination of the unit electric motors to be energized to control driving force and the speed of a car.

CONSTITUTION: With a motor-driven driver 21 suspended at the lower part of the body-frame of a motorcycle, an output shaft 23 is rotatably supported across the width of the motorcycle at the center part of a nearly cylindrical case 22. In the case 22, four unit electric motors 241-244 are arranged circumferentially in equal intervals around the output shaft 23 by a frame member 25. On the end part of the output shaft 23 projected from the case 22, a drive sprocket 26 is installed. Each unit electric motor 24 is a direct current motor, and composed of a well-known rotary shaft 30, a rotor 31, and a stator 32. A coil of each stator 32 is connected through a switching circuit 36 to a drive circuit (not shown). Further, each rotary shaft 30 is connected through a centrifugal clutch 34 to a pinion 35 at the right end, and the pinion 35 is engaged with a gear 27 on the output shaft 23.