A power transmission apparatus configured for a vehicle, may include a motor/generator including a motor shaft a first input shaft selectively connectable to the motor shaft, a second input shaft externally disposed with the first input shaft and selectively connectable to the motor shaft, a third input shaft externally disposed with the second input shaft and selectively connectable to the motor shaft, a first torque mediating shaft formed as a hollow shaft and coaxially and externally disposed with the first input shaft without rotational interference therebetween, an intermediate shaft parallel with the first input shaft, a first shifting section receiving a torque and outputting the shifted torque, and a second shifting section including a first planetary gear set selectively receiving the torques from the first shifting section and the third input shaft, respectively, and outputting shifted torque through one gear set.