A power transmission apparatus configured for a vehicle, may include a first input shaft selectively connectable to an engine output shaft, a second input shaft mounted coaxial with the first input shaft and selectively connectable to the engine output shaft, a third input shaft external to the second input shaft and selectively connectable to the engine output shaft, a torque mediating shaft mounted coaxial with the first input shaft, first and second intermediate shafts, an idle shaft, a first shifting section including five gear sets, the first and second intermediate shafts, the torque mediating shaft and the idle shaft, a second shifting section including a planetary gear set having a sun gear fixedly connected to the torque mediating shaft, and an output shaft mounted coaxial with and selectively connectable to the first intermediate shaft and outputting a torque from the first and second shifting sections.