Patent ID: 8657286

Claim:
A sheet stacking apparatus on which sheets discharged from an image forming portion are stacked, comprising: first and second sheet-stacking trays configured to stack thereon the sheets discharged from said image forming portion, said first and second sheet-stacking trays being capable of being separately taken out of the sheet stacking apparatus with sheets stacked thereon; a control unit configured to cause selective execution of one of a first stacking mode in which sheets having a size not larger than a predetermined size are caused to be stacked on one of said first and second sheet-stacking trays, and a second stacking mode in which sheets having a size larger than the predetermined size are caused to be stacked in a state extending on said first sheet-stacking tray and said second sheet-stacking tray; a detection unit configured to detect whether each of said first and second sheet-stacking trays is set or taken out; and a display unit, wherein, in a case where the second stacking mode is selected: (i) if said detection unit detects that both of said first and second sheet-tracking trays are set, said control unit is configured to allow the sheets to be stacked in the second stacking mode; (ii) if said detection unit detects that one of said first sheet-stacking tray or said second sheet-stacking tray is taken out, said control unit is configured to control said display unit to display a message advising setting said first sheet-stacking tray or said second sheet-stacking tray, whichever has been taken out, and to inhibit the sheets from being stacked in the second stacking mode until said detection unit detects that both of said first and second sheet-tracking trays are set; and (iii) if said detection unit detects that both of said first and second sheet-tracking trays are taken out, said control unit is configured to control said display unit to display a message advising setting both of said first and second sheet-tracking trays which have been taken out, and to inhibit the sheets from being stacked in the second stacking mode until said detection unit detects that both of said first and second sheet-tracking trays are set, and wherein, in a case where, during execution of a first job of stacking the sheets in the first stacking mode, a second job of stacking the sheets is reserved in the second stacking mode, if said detection unit detects that one of said first sheet-stacking tray or said second sheet-stacking tray is taken out, said control unit is configured to control said display unit to display a message advising setting said first sheet-stacking tray or said second sheet-stacking tray, whichever has been taken out.