To provide a supporting structure of a driving force transmitting device capable of preventing the occurrence of swing due to play by a simple configuration.

This driving force transmitting device 6 is supported in a differential carrier 9 by supporting a shaft part 41 by a second bearing 35 through a pinion gear 32 and supporting a small diameter part 42 by a first bearing 34. The first and second bearings 34, 35 can support radial load and axial load, and predetermined pre-load is applied on the first and second bearings 34, 35 along the directions of axial lines L0 being reverse for each other.