Abstract: A sheet separation device that conveys a two-ply sheet in a state where the one side joined is located on an upstream side or a downstream side of the two-ply sheet in a conveyance direction, separates the two-ply sheet into the two sheets, and inserts an inner sheet from a non-joined side opposite the joined side in the sheet conveyance direction so that the inner sheet is sandwiched between the two sheets overlaid with each other includes a conveying roller pair including a pair of rollers and circuitry. The conveying roller pair conveys the two-ply sheet and holds a joined portion of in the two-ply sheet at which the two sheets are joined, at a nip portion of the conveying roller pair when the inner sheet is inserted into the two-ply sheet. The circuitry contacts the inner sheet against the joined portion of the two-ply sheet to perform skew correction.