A differential device includes: a differential gear mechanism; and an integrated differential case housing the mechanism, the differential case including bearing bosses formed integrally on one and other side portions thereof and aligned on a same axis to be rotatably supported by a transmission case; a work window being provided in the differential case; sleeves rotatably supported by the bosses and connected to side gears of the mechanism liquid-tightly. The sleeves can be passed through an inside of the differential case from the window and fitted and inserted to inner peripheries of the bosses, sleeve retainers are provided between the sleeves and the bosses, and seal devices for preventing lubricating oil in the differential case from flowing out are provided between the side gears and the sleeves. Accordingly, when drive shafts are removed from the differential device, the oil in the transmission and differential cases does not flow out.