A power transmission apparatus for a vehicle may include a first input shaft fixedly connected to an engine output shaft, a second input shaft coaxial with the first input shaft a third input shaft coaxial with the second input shaft, an intermediate shaft and at least one output shaft, a planetary gear set mounted on an axis of the intermediate shaft, a plurality of gear sets, each of which allows at least one torque flow between the intermediate shaft, the first, second, and third input shafts, the output shaft and the planetary gear set, a first synchronizer mounted on the output shaft, selectively receiving a torque from the second input shaft, a second synchronizer mounted on the output shaft, selectively receiving a torque from the third input shaft through two paths, and transmitting the received torque to the output shaft, and four clutches each of which facilitating selective connection.