To make it possible to reduce generation of errors such as jamming and loading failures.

In a post-processing device, a control circuit 213 acquires either of first information indicating the number of sheets constituting a sheet bundle formed by staple means 212 and/or a kind of the sheets, or second information indicating a volume of the sheet bundle loaded on an ejection tray 25. Then, the control circuit 213 determines a gap (L1-L2) in the sheet width direction of a staple position and a pressing position by a pressing member 26 in the sheet bundle on the basis of either of the acquired first information or second information. The control circuit 213 further changes at least one of the staple position and the pressing position by the pressing member 26 on the ejection tray 25 to attain the determined gap (L1-L2) in the sheet width direction.