Abstract: A planetary gear mechanism comprises a sun gear, a planetary gear that meshes with the sun gear, a planetary carrier having a planetary shaft which axially supports the planetary gear, and a ring gear which meshes with the planetary gear; wherein: the planetary gear has a coaxially disposed first inside-diameter part and second inside-diameter part of different inside diameter; the planetary gear mechanism has a first bearing member that has an outside diameter conforming to the first inside-diameter part and a second bearing member that has an outside diameter conforming to the second inside-diameter part, the two bearing members being arranged between the planetary shaft and the planetary gear; and the planetary gear mechanism is easily assembled while having a configuration in which the two bearing members are interposed between the planetary shaft and the planetary carrier so as to be coaxially divided in the axial direction.