Patent ID: 8172215

Claim:
A sheet stacking apparatus comprising: a sheet stacking unit which stacks sheets conveyed by a sheet conveyance device; three sheet extraction portions which allow to selectively extract the sheets stacked on said sheet stacking unit from one of three directions including a downstream side of a sheet conveyance direction and two directions perpendicular to the sheet conveyance direction; a plurality of first detection sensors which are provided in at least two of said three sheet extraction portions to detect an object that enters said sheet stacking unit; a second detection sensor which detects a moving direction of the sheets stacked on said sheet stacking unit; and a control device which stops an operation of the sheet conveyance device when at least one of said plurality of first detection sensors detects the object, and disables a detection operation of at least one of said first detection sensors corresponding to the moving direction of the sheets when said second detection sensor detects the moving direction of the sheets.