A vehicle driving device comprising: a rotary electric machine that is a driving force source of a first wheel and a second wheel; a speed reduction device that reduces a speed of a rotation of the rotary electric machine; and a differential gear device that distributes to the first wheel and the second wheel, a driving force that is transmitted from the rotary electric machine via the speed reduction device, wherein the speed reduction device and the differential gear device are disposed coaxially with the rotary electric machine, the speed reduction device has a first planetary gear mechanism and a second planetary gear mechanism, the first planetary gear mechanism is disposed on the rotary electric machine side relative to the second planetary gear mechanism in an order of a power transmission path, and the first planetary gear mechanism is disposed on the rotary electric machine side relative to the second planetary gear mechanism along an axial direction, a helix angle of a helical tooth of the first planetary gear mechanism and a helix angle of a helical tooth of the second planetary gear mechanism are formed so that a thrust force of the first planetary gear mechanism and a thrust force of the second planetary gear mechanism are in mutually opposite directions in the axial direction, and a first gear width that is a width of a gear of the first planetary gear mechanism along the axial direction is smaller than a second gear width that is a width of a gear of the second planetary gear mechanism along the axial direction, characterized in that a first speed reduction ratio that is a speed reduction ratio of the first planetary gear mechanism is set to be larger than a second speed reduction ratio that is a speed reduction ratio of the second planetary gear mechanism, and the second gear width is smaller than a length obtained by multiplying the first gear width by the first speed reduction ratio. a rotary electric machine that is a driving force source of a first wheel and a second wheel; a speed reduction device that reduces a speed of a rotation of the rotary electric machine; and a differential gear device that distributes to the first wheel and the second wheel, a driving force that is transmitted from the rotary electric machine via the speed reduction device, wherein the speed reduction device and the differential gear device are disposed coaxially with the rotary electric machine, the speed reduction device has a first planetary gear mechanism and a second planetary gear mechanism, the first planetary gear mechanism is disposed on the rotary electric machine side relative to the second planetary gear mechanism in an order of a power transmission path, and the first planetary gear mechanism is disposed on the rotary electric machine side relative to the second planetary gear mechanism along an axial direction, a helix angle of a helical tooth of the first planetary gear mechanism and a helix angle of a helical tooth of the second planetary gear mechanism are formed so that a thrust force of the first planetary gear mechanism and a thrust force of the second planetary gear mechanism are in mutually opposite directions in the axial direction, and a first gear width that is a width of a gear of the first planetary gear mechanism along the axial direction is smaller than a second gear width that is a width of a gear of the second planetary gear mechanism along the axial direction, characterized in that a first speed reduction ratio that is a speed reduction ratio of the first planetary gear mechanism is set to be larger than a second speed reduction ratio that is a speed reduction ratio of the second planetary gear mechanism, and the second gear width is smaller than a length obtained by multiplying the first gear width by the first speed reduction ratio.