Sheet post-processing apparatus having excellent sheet stacking capability

A discharging and stacking method of a sheet post-processing apparatus which stacks a sheet on a process tray, stacks the sheet discharged from the process tray on a storage tray, and rotates a paper discharge roller provided at the end of the process tray in a sheet discharging and conveying direction and a bundle discharge belt having a bundle hook for discharging and conveying the sheet in the storage tray direction so as to discharge the sheet to the storage tray,

• wherein the sheet is conveyed in the state where a first tangential speed at which the paper discharge roller conveys the sheet in the storage tray direction and a first movement speed of the bundle hook are identical with each other, and
• during a sheet stacking operation in which the bundle hook passes from the discharge start position to the sheet rear end contacting member of the process tray,
• wherein the paper discharge roller rotates at a second tangential speed slower than the first tangential speed and the bundle hook moves at a second movement speed slower than the second tangential speed until the bundle hook moves from a discharge start point to a discharge end position of the sheet during a sheet stacking operation in which the bundle hook passes from a discharge start position to a sheet rear end contacting member of the process tray, and
• wherein the paper discharge roller is stopped and the bundle hook moves at a third movement speed slower than the second movement speed after the bundle hook reaches the discharge end position.