A power transmission apparatus includes: a first input shaft always receiving an input torque from an engine; second and third input shafts coaxially disposed and selectively connected with the first input shaft; a torque mediating shaft selectively connected with the first input shaft or a transmission housing; first and second intermediate shafts and an output shaft respectively disposed in parallel with the first input shaft; a first preliminary shifting section receiving a torque through a first input gear set, selectively shifting the received torque, and outputting the shifted torque; a second preliminary shifting section including a second shifting gear set which outputs a torque from the first input shaft and stops; and a compound shifting section forming an output torque by the input torque and the first and second shifted torques.