PURPOSE: To provide an epicycle reduction gear, which has a compact form in the direction of a shaft, and which is free from backlash.

CONSTITUTION: A first reduction mechanism on an input side and an epicycle reduction mechanism on an output side are arranged in the same box, and the first reduction mechanism is formed exchangeable on the input side of a box body 1. The epicycle reduction mechanism is divided into halves on a vertical plane with internal gears 11, 12 serving as axes and the divided internal gears 11, 12 are displaced from one another along the vertical plane, so as to eliminate any backlash between them and an epicyclic gear 9. A bearing is provided between the outer periphery of a carrier 10 for holding the epicyclic gear 9 and the inner surface of the box body 1, so as to shorten the entire length.