Powertrain of vehicle

A power transmission device is provided with a differential case including an outer case for receiving torque and rotating about an axis and an inner case rotatable relative to the outer case, a clutch member fixed to or engaged with the outer case and structured so that the clutch member and the inner case form a dog clutch, the clutch member transmitting the torque from the outer case to the inner case when the dog clutch is in mesh, and a differential gear set. The gear set includes side gears rotatable about the axis and capable of making a differential motion relative to each other and forming a friction clutch in combination with the differential case, and a pinion gear supported by the inner case as to transmit the torque to the side gears and meshed with the side gears to allow the differential motion.