An image forming apparatus can facilitate a determination whether a sheet having an image formed thereon, which is discharged by a designated processed job, is allowed to be taken out or not. The image forming apparatus determines whether or not the sheet having the image formed thereon discharged by the designated processed job is stacked on a stacking unit on which the sheet having the image formed thereon discharged by a job currently performing image forming processing, based on stack state information which can be updated in real time. When a sheet having the image formed thereon is not allowed to be taken out, the image of the portion corresponding the sheet is highlighted. Further, a waiting time is displayed on the display.