A power transmission device for a commercial vehicle having an electric axle, may include a first differential ring gear fixedly mounted on a first rear-wheel driveshaft; a second differential ring gear mounted on a second rear-wheel driveshaft; a propeller shaft, with a first differential drive gear engaged with the first differential ring gear being connected to a front-end portion of the propeller shaft and a second differential drive gear engaged with the second differential ring gear being connected to a rear end portion thereof; a reducer connected to the first differential ring gear or the propeller shaft; and a motor, an output shaft of the motor being connected to an input gear of the reducer.