PURPOSE: To eliminate a differential gear unit for producing a differential rotational speed between right and left wheels, by inverse-proportionally changing the effective radii of the right and left wheels on travelling of a vehicle.

CONSTITUTION: A bearing 4 for journalling an axle 3 is integrally incorporated in the lower section of a bearing arm 2. A projectile shape axle 5 having its diameter decreasing outward is attached to the axle 3. The bearing arm 2 is connected to a steering rack 11 through a connecting rod 10 to rotate a bearing arm 1 around a pin 2 through the rack 11 and the connecting rod 10 when a steering wheel 12 is turned. The ground contact points of wheels 5, 5' attached to the axles are different from each other in dependence upon the tilting angle of the arm 1, thereby the vehicle may be turned. The bevel gear 9 transmits power from a motor to a drive shaft 7.