A friction device assembly structure for an automatic transmission includes a first friction device and an end play adjustment element. The first friction device includes a plurality of discs and a plurality of plates which are alternately arranged and configured such that a frictional force is created between the discs and the plates by the pressing force of a piston. The end play adjustment element is provided on an end of the first friction device to adjust an end play defined between the first friction device and the piston. The end play adjustment element is hollow such that an inner diameter thereof is greater than an outermost diameter of a second friction device which is provided inside the first friction device. Thereby, the end play adjustment element is able to be assembled without any interference from the second friction device.