A carrier includes a first carrier portion and a second carrier portion. The first carrier portion includes a gear housing space that houses a planetary gear, an opening that opens the gear housing space toward the second carrier portion and allows the planetary gear to fit into the gear housing space, and a first support hole that supports a first end portion of the planetary support shaft. The second carrier portion includes a cover portion that covers the opening, a second support hole that supports a second end portion of the planetary support shaft, and a joining portion that detachably joins the second carrier portion to the first carrier portion. The joining portion is joined to the first carrier portion by being tightened in a direction aligned with a direction of an axial core of a sun gear.