A brake (B2) of an automatic transmission (20) locks a second ring gear (22r) of a second planetary gear (22) so as not to be rotatable, and is provided with: a friction plate (601) and a separator plate (602); and a drum member (360) as a brake hub that is constantly coupled to the second ring gear (22r) and that is rotatably supported by an inner cylindrical part (115) of a center support (11c) between the friction plate (601) and the like and the second planetary gear (22). The drum member (360) and the second ring gear (22r) are coupled via a spline.