A driving force distribution device includes a first friction roller that rotates together with a rotating member constituting a torque-transmitting path to the main driving wheel; a second friction roller that rotates together with a rotating member constituting a torque-transmitting path to the auxiliary driving wheel; and an inter-roller radial press section that presses the first and second friction rollers in radial directions of the first and second friction rollers into pressing contact with one another, to allow torque transmission between the first and second friction rollers, wherein the inter-roller radial press section sets a radial pressing force between the first and second friction rollers to limit torque input to the auxiliary driving wheel by allowing slippage between the first and second friction rollers when a maximum torque is inputted to the driving force distribution device under a condition that torque distribution to the auxiliary driving wheel is maximized.