Patent ID: 8074984

Claim:
A sheet stacking apparatus which is attachable to an image forming apparatus that executes a job for forming an image on a sheet, and which stacks sheets ejected from the image forming apparatus, the sheet stacking apparatus comprising: a stage to receive a sheet ejected from the image forming apparatus; a sheet detection device to detect whether or not any sheet is present on the stage; a driving section to move the stage; and a control section to control the driving section to move the stage; wherein, in a case in which job attribute information set in the image forming apparatus indicates that the job executed by the image forming apparatus is a mixing prohibition job, the control section controls the driving section to move the stage to a sheet removing position automatically, when an output of the sheet detection device indicates that a sheet of a previous job is present on the stage, so as to prevent the sheet of the mixing prohibition job from mixing with the sheet of the previous job; and wherein in a case in which job attribute information set in the image forming apparatus indicates that the job executed by the image forming apparatus is not a mixing prohibition job, the job is executed irrespective of whether the sheet of the previous job is present on the stage.