A power transmission apparatus configured for a vehicle may include a first input shaft fixedly connected to a motor/generator, a second input shaft selectively connectable to the first input shaft, a third input shaft selectively connectable to the first input shaft, a torque mediating shaft externally disposed with the first input shaft, an intermediate shaft, an idle shaft, an output shaft, a first shifting section selectively receiving a torque from the third input shaft, shifting the received torque and outputting the shifted torque, a second shifting section shifting a torque from the first input shaft to the torque mediating shaft, or stopping a rotation of the torque mediating shaft, and a third shifting section selectively receiving a torques from the first and second shifting sections and a torque from the second input and outputting shifted torque to the output shaft.