A power transmission apparatus for a vehicle may include a first input shaft adapted to selectively receive torque of an engine, a second input shaft disposed without rotational interference with the first input shaft, a third input shaft disposed in a row with the second input shaft and without rotational interference with the first input shaft, a planetary gear set including a first rotation element, a second rotation element directly connected to the third input shaft, and a third rotation element directly connected to the first input shaft, a motor/generator directly connected to the first rotation element, a first speed output unit adapted to convert torque input from the second input shaft or the third input shaft and output the converted torque, and a second speed output unit adapted to convert torque input from the second input shaft or the third input shaft and output the converted torque.