A power transmission apparatus for a vehicle may include a first input shaft directly connected to a motor/generator, a second and third input shafts coaxial and selectively connectable to the first input shaft, a torque mediating shaft coaxial with the first input shaft, an intermediate shaft and output shaft disposed in parallel with the first input shaft, a first shifting section receiving torque from the third input shaft and outputting a modified torque to the torque mediating shaft, a second shifting section including first planetary gear set, shifting torque of the first input shaft to output the shifted torque to the torque mediating shaft, and selectively stopping the torque mediating shaft, and a third shifting section including second planetary gear set, forming an output torque in combination of torques from the first and second shifting sections and the second input shaft, and outputting the output torque to the output shaft.