A differential device of a four-wheel drive vehicle which is operated in selected one of a two-wheel drive state in which a drive force from a drive power source is transmitted to left and right main drive wheels and a four-wheel drive state in which a drive force from the drive power source is transmitted to the left and right main drive wheels and left and right auxiliary drive wheels, the differential device including a disconnect mechanism with which a power transmission member for transmitting a drive force only to the auxiliary drive wheels in the four-wheel drive state is separated from the auxiliary drive wheels in the two-wheel drive state, the differential device comprising: a cylindrical ring gear supported rotatably around one rotation axis by a case; a differential case including one and the other cylindrical end portions in a rotation axis direction of the ring gear and supported at the one end portion by the ring gear and at the other end portion by the case rotatably and concentrically with the rotation axis; a sleeve fitted movably in the rotation axis direction in a power transmittable manner on the inner circumferential side of the one end portion of the differential case; and an actuator driving the sleeve via a thrust transmission mechanism between an engagement position at which outer circumferential teeth formed on the sleeve are engaged with inner circumferential teeth formed on the inner circumferential side of the ring gear and a release position at which the teeth are not engaged, the thrust transmission mechanism being at least partially located in a radial space between the ring gear and an axle penetrating the ring gear or a rotation shaft integrally rotating with the axle.