PURPOSE: To obtain a differential gear device with which the sufficient strength and the allowable transmission torque can be obtained, loosening of bolts is suppressed, and the outside diameter can be reduced even in the case where a bevel gear is installed.

CONSTITUTION: An annular gear part 31 is integrally formed on the outer peripheral part of the case body 25 of a differential gear device which is constituted so that a differential mechanism which is formed by differential connecting a right rear axle 11 and a case 23, left rear axle 13 and the case 23, right rear axle 11 and the left rear axle 13 is accommodated into the case 23 consisting of a case body 25 and a cover 27, and the cover 27 is installed on the case body 25 by bolts 36, at the annular gear part 31.