A power transmission device is used to distribute torque from a power source (ENG) to an external device and an auxiliary device. The power transmission device is comprised of a first bearing (55) and a second bearing (12) both secured to a stationary member, a first sprocket (51) rotatably supported by the first bearing (55), a second sprocket (52) capable of being drivingly coupled with the auxiliary device, a chain (53) coupling the first sprocket (51) with the second sprocket (52), a rotary shaft (5) rotatably supported by the second bearing (12), which is drivingly coupled with the power source and drivingly engageable with the external device to transmit a first part of the torque to the external device, and a joint drivingly linking the rotary shaft (5) with the first sprocket (51) to transmit a second part of the torque to the first sprocket (51).