To provide a power transmission device for a vehicle capable of performing regeneration by an auxiliary power source when the vehicle is stopped, and smoothly starting.

This power transmission device includes: a planetary gear mechanism 5 having a sun gear 5s, a carrier 5c and a ring gear 5r to change speed of torque of an input member 1 and to transmit the torque to an output member 8; the auxiliary power source 11 capable of performing power running and regeneration; and an energy storage means 21 for supplying energy during the power running and recovering energy during the regeneration. In the power transmission device, input member 1 and the sun gear 5s are connected via a first one-way clutch 10 allowing only torque transmission to the sun gear 5s, the output member 8 and the carrier 5c are connected so that the torque may be transmitted, and the auxiliary power source 11 and the ring gear 5r are connected via a second one-way clutch 12 allowing only torque transmission to the ring gear 5r and a clutch 14 for regeneration selectively allowing torque transmission to the auxiliary power source 11.