To simplify structure and to need only a comparatively small structure space.

A planetary gear device is provided with a planetary carrier 24 relatively non-rotatably arranged on a drive shaft 18. The planetary carrier 24 supports an inner planetary gear 26 rolling on the outer periphery of a sun gear 12, and the inner planetary gear 26 is coupled to an outer planetary gear 34 supported revolvably centering around the center of the rotary axis of the inner planetary gear 26. The outer planetary gear 34 is rolled along a hollow gear relatively non-rotatably arranged on a driven shaft, and besides a hollow gear is provided with an internal tooth ring 40 and an external tooth ring 34. The outer planetary gear 34 is rolled along the internal tooth ring 40 or the external tooth ring 42 of the hollow gear in relation with the input number of rotion nE of the drive shaft 18.