A power transmitting apparatus includes: an electric supplementary drive unit; a torque converting device including a planetary gear set having a first rotation element connected to the electric supplementary drive unit, a second rotation element connected to an engine, and a third rotation element operated as an output element; an input device including a first input shaft selectively connected to the second rotation element through one clutch and provided with at least one input gear fixedly disposed thereon, and a second input shaft disposed on the same axis as the first input shaft without rotational interference with the first input shaft, directly connected to the third rotation element, selectively connected to the second rotation element through the other clutch, and provide with at least one input gear fixedly disposed thereon; and a speed output device converting torque of the input device and outputting the converted torque.