A power transmission apparatus includes a first input shaft selectively receiving an input torque, a second input shaft coaxially disposed with the first input shaft and selectively receiving the input torque, first and second intermediate shafts selectively interconnected and disposed in parallel with the first input shaft, a torque mediating shaft coaxially disposed with the first input shaft, a preliminary shifting section receiving a torque through a first input shaft and selectively outputting a shifted torque to the second intermediate shaft, a compound shifting section including a planetary gear set having a sun gear fixedly connected with the torque mediating shaft, a planet carrier fixedly connected with the second input shaft, and a ring gear externally gear-meshed with the second intermediate shaft, and an output shaft receiving a torque received from the compound shifting section and transmitting the received torque to a differential.