A power transmission apparatus for a vehicle may include a first input shaft directly connected with a motor/generator, second and third input shafts and torque mediating shaft coaxial and selectively connected with the first input shaft, a first intermediate shaft and first and second idle shafts in parallel with the first input shaft, a second intermediate shaft in parallel with the first input shaft, and selectively connected with a transmission housing, an output shaft in parallel with the first input shaft, and coaxial and selectively connected with the second intermediate shaft, a first shifting section including six gear sets, selectively receiving torque through the first and third input shafts, and outputting intermediate shift-stages, and a second shifting section including a planetary gear set, forming an output torque by combination torques from the first shifting section and the second input shaft, and outputting the output torque to the output shaft.