To provide a driving shaft reduction gear which is high in durability, regarding the driving axle reduction gear to transmit rotation of a driving axle to a driven element through a planetary gear mechanism.

In the driving shaft reduction gear, rotation of a driving shaft 2 is transmitted to a wheel hub 11 through a planetary gear mechanism. A ring gear hub 15 situated at a first ring gear 5 in the planetary gear mechanism is hooked on a bearing holder 23 attached to an axle housing 20 through a division ring 18. The constitution regulates axial movement of a first ring gear 5. Further, a shaft part 25 mounted on a ring gear hub 15 is unrotatably supported by the inner peripheral surface of a shaft end part 21 of an axle housing 20.