PURPOSE: To provide a reduction and differential gear device for a vehicle, having a falling restraining means, capable of effectively preventing a breakage or abnormal abrasion of teeth of a reduction pinion and a reduction gear and free from maintenance and adjustment for a long time.

CONSTITUTION: A falling restraining device 54 which abuts against the back surface 46 of a meshing portion of a reduction gear 38 so as to prevent falling due to meshing reaction force of the reduction gear 38 comprises a support member 56 disposed detachably in a differential case 32, an abutting pin 60 screwed in the support member 56 so as to advance toward the back surface 46 of the meshing portion of the reduction gear 38 according to one-way rotation, and a torsion spring 66 interposed between the support member 56 and the abutting pin 60 and energizing the abutting pin 60 in the rotating direction.