Abstract: The rotary flat membrane separation apparatus comprises: a plurality of hollow rotary shafts; a plurality of rotary flat membrane disks mounted on each of the plurality of hollow rotary shafts at regular intervals, the plurality of rotary flat membrane disks mounted on adjacent two of the plurality of hollow rotary shafts being alternately arranged side by side in equal intervals; and a plurality of collars, each of the plurality of collars being arranged between adjacent two of the plurality of rotary flat membrane disks mounted on each of the plurality of hollow rotary shafts. The apparatus is characterized in that a diameter of the collars is between 0.18-0.34 times a diameter of the rotary flat membrane disks. Thus, the effective membrane area can be as large as possible while preventing the vibration of the rotary flat membrane disks caused by the rotation.