Patent ID: 7377511

Claim:
A sheet stacking apparatus, comprising: a stack tray onto which sheets discharged from an outlet are stacked; a driving device which drives the stack tray to ascend and descend; a sheet surface detecting device which detects a top surface of the sheets stacked on the stack tray at a stacking position at which the sheets discharged from the outlet are stacked; a height controlling portion which controls said driving device to move the stack tray to the stacking position in such a way that the top surface detected by said sheet surface detecting device maintains a constant height; and a time measuring portion which measures time; a standby controlling portion which causes the stack tray to stop when said time measuring portion detects the lapse, from a start of movement, of a time period for a moving operation that is calculated based on a predetermined distance of movement of the stack tray and a moving speed where the stack tray moves the predetermined distance.