A sheet post-processing apparatus 100 includes bundle discharge rollers 6, a sheet detection sensor 31, a main tray 11, and a sheet hold device 32 having a plurality of hold portions 34a to 34c. When a sheet bundle is discharged from the bundle discharge rollers 6, the hold portions 34a to 34c rotate to a release position where the hold portions 34a to 34c stop holding the sheet bundle P stacked on the main tray 11, the main tray 11 moves downward to a wait position H2, and then, the hold portions 34a to 34c rotate to the lowest position, then the main tray 11 moves up to a hold position H1.