To provide a light-weighed free running differential device capable of certainly changing a driving state by improving the free running differential device without requiring an inner case and a slide gear.

In a device for torque-distributing and transmitting a rotation- driving force of a differential case 1 to right and left side gears 5, 6 disposed on a rotation shaft of the differential case 1 through differential gears 3, 4, a pinion shaft 3 in the differential gears 3, 4 is attachably/detachably mounted on an inner periphery of the differential case 1 and a connection/disconnection of the rotation-driving force from the differential case 1 to the differential gears 3, 4 is carried out. Thereby, since a whole device is made light-weighed without requiring an inner case and a cam ring such as in a conventional device and a space required for the inner case can be occupied by a pinion gear, the pinion gear itself ensures a size to some degree. A sufficient driving force can be transmitted even by light and simple 2-pinion gear type differential gear.