A sheet processing apparatus nicely performs an aligning operation for a sheet conveyed onto a process tray with a simple configuration. A switching member performs an operation of switching an aligning member from a non-contact state to a contact state before the sheet reaches a contact position on the tray or performs an operation of, while the sheet on the tray is being conveyed toward a sheet edge regulating member by the aligning member, switching the aligning member from the contact state to the non-contact state, and further switching the aligning member from the non-contact state to the contact state. Thus, the sheet processing apparatus reduces an occurrence of a conveyance failure caused by collision of a leading edge of thick paper with a return roller and a return guide member, and maintains good conveyance performance by preventing sheet stick caused by a coating material coated on coat paper.