A power transmission apparatus may include a first input shaft having at least one input gear and selectively connected to a power source through a first clutch, a second input shaft having at least one input gear and selectively connected to the power source through a second clutch, a first speed output unit including a first output shaft and at least one speed gear engaged with the at least one input gear on the first and second input shafts, a second speed output unit including a second output shaft and at least one speed gear engaged with the at least one input gear on the first and second input shafts and rotatably disposed on the second output shaft, and an idle module including at least two idle gears on an idle shaft.