Sheet processing apparatus

A sheet processing apparatus, comprising:

• a transport unit that is controlled to transport a first sheet to a first position, transport a second sheet to a second position, which is displaced to an upstream side of a sheet transport direction relative to the first position, after the second sheet has been superimposed on the first sheet, and transport a third sheet to a third position, which is displaced to a downstream side of the sheet transport direction relative to the second position, after the third sheet has been superimposed on the second sheet;
• a holding unit that is controlled to hold the first sheet at the first position when the transport unit transports the second sheet to the second position, and hold the second sheet at the second position when the transport unit transports the third sheet to the third position;
• and
• a sheet transport guide that guides the first, second, and third sheets towards the transport unit and the holding unit, the sheet transport guide including a sheet supporting surface,
• wherein the holding unit includes a presser member that is openable and closable with respect to the sheet supporting surface, an outlet roller near an outlet portion of the sheet transport guide and having a friction member in at least a circumferential surface thereof, and a rotation regulation unit that regulates rotation of the outlet roller to make the outlet roller unrotatable,
• wherein the presser member is closed to press any sheets on the sheet supporting surface against the sheet supporting surface, and is opened by moving away from the sheet supporting surface,
• wherein, to transport the first sheet to the first position, the transport unit transports the first sheet in an opposite direction to the sheet transport direction while the presser member is opened, to insert the first sheet between the sheet supporting surface and the presser member, and
• wherein, to transport the second sheet to the second position, the transport unit transports the second sheet in the opposite direction to the sheet transport direction while the presser member is opened and the rotation regulation unit makes the outlet roller unrotatable, to insert the second sheet between the sheet supporting surface and the presser member and hold the first sheet in place at the first position against the friction member.