In a differential gear device including: a differential casing rotatable about an axis and having a pair of through-holes; a pinion shaft accommodated within the differential casing and extending through the through-holes; a pair of pinion gears fitted on an outer circumferential surface of the pinion shaft such that the pinion gears are rotatable relative to the pinion shaft; a pair of side gears meshing with the pinion gears; and a pair of pinion washers interposed between the differential casing and the respective pinion gears, each of the pinion washers has a retainer structure partially inserted through a gap formed between an inner circumferential surface of a corresponding one of the through-holes and the outer circumferential surface of the pinion shaft. The retainer structure is held in contact with a corresponding axial end face of the pinion shaft, to prevent axial movements of the pinion shaft.