Abstract: An improved electrically powered driving mechanism for use on a bicycle can be readily mounted onto a common bicycle without making any additional conversion work. It is particularly designed to improve the inefficiency of a conventional friction-type transmission of an electrically powered driving mechanism. It has a dual-purpose power transmitting device having a pair of wheels adapted for either friction transmission or gear engagement transmission. Each driving wheel is divided into two sides, one side for frictional transmission and the other side equipped with a plurality of consecutively spaced gear teeth for gear engagement transmission so that the wheels can be selectively assembled to make the driving device to be either frictionally operable or gear drivable. Besides, a dual-shaft electric motor provides power to the driving mechanism. Between the driving device and the dual-shaft electric motor is disposed a pair of shifting gear sets.