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 (L), 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 (SF1) of the first planetary gear mechanism and a thrust force (SF2) of the second planetary gear mechanism are in mutually opposite directions in the axial direction (L), and a first gear width (W1) that is a width of a gear of the first planetary gear mechanism along the axial direction (L) is smaller than a second gear width (W2) that is a width of a gear of the second planetary gear mechanism along the axial direction (L), 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 (W2) is smaller than a length obtained by multiplying the first gear width (W1) 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 (L), 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 (SF1) of the first planetary gear mechanism and a thrust force (SF2) of the second planetary gear mechanism are in mutually opposite directions in the axial direction (L), and a first gear width (W1) that is a width of a gear of the first planetary gear mechanism along the axial direction (L) is smaller than a second gear width (W2) that is a width of a gear of the second planetary gear mechanism along the axial direction (L), 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 (W2) is smaller than a length obtained by multiplying the first gear width (W1) by the first speed reduction ratio. <EOS>