A sheet processing device sandwiches a sheet-shaped medium in a two-ply sheet in which two sheets are overlaid and partially bonded. The sheet processing device includes a separator, a conveyor, and a switching member. The separator separates the two sheets of the two-ply sheet. The conveyor is disposed downstream from the separator in a sheet conveyance direction and conveys the two-ply sheet. The switching member is disposed downstream from the conveyor in the sheet conveyance direction. The switching member switches a conveyance path of the two-ply sheet to convey the two-ply sheet to a fixing path on which fixing processing is performed on the two-ply sheet or a non-fixing path on which no fixing processing is performed on the two-ply sheet.