PURPOSE: To reduce the backlash in the entire differential gear device, and to enhance operational feeling by moving element gears forming pairs in such a way that they are detached from the tooth surfaces on the one side of side gears and are brought near to the tooth surfaces on the other side thereof, and by fixing the positions of the element gears after movement.

CONSTITUTION: In a differentiaI gear device provided with a pair of side gears 2 (2A, 2B) and two pairs of element gears 4 (4A, 4B) and 5 (5A, 5B), when it is assembled, after the positions of the pair of element gears 5 (5A, 5B) have been fixed, the pair of element gears 4 (4A, 4B) are moved in the X direction or in the axial direction of the side gears 2 (2A, 2B). Thereby, the tooth surfaces (41A, 41B) of the respective gears 4 (4A, 4B) are brought near to the tooth surfaces (21A, 21B) of the respective gears 2 (2A, 2B), and the tooth surfaces (51A, 51B) of the gear 5 (5A, 5B) are brought near to the tooth surfaces (22A, 22B) of the respective gears 2 (2A, 2B) for fixing the entire positioning. Then, by fixing the positions of the gears 4 (4A, 4B), the tooth surfaces (41A, 41B; 51A, 51B) of the respective gears 4, 5 are maintained in the condition that they are brought into contact with the tooth surfaces (21A, 21B; 22A, 22B) of the side gears 2A, 2B.