A continuously variable transmission comprises a drive shaft which has first and second drive shafts and is provided with rotational power, a planetary gear unit which is meshed with the first drive gear of the drive shaft and has a sun gear secured to an output shaft, and a transmission which receives a portion of driving force to provide additional output. Interruption of power transmission when shifting is prevented. Also, since the construction of the continuously variable transmission is simplified to minimize the load generated due to a shifting operation, power loss resulting from shifting is reduced, and the manufacturing cost is decreased. In particular, since vibration and noise generated upon shifting are decreased, the continuously variable transmission can be widely applied, from a small power device such as a bicycle or a motorcycle to a large power transmission apparatus such as an industrial machine.