Patent ID: 7874552

Claim:
A sheet post-process apparatus, comprising: a static stack tray for stacking a first sheet; a movable stack tray for stacking a second sheet and movable to different vertical positions above, below, and equal to a predetermined first height; a movable tray position detection unit that detects a first position of the movable stack tray while a request command for post-processing of the sheet is not received; an upper surface sensor that senses either an upper surface of the movable stack tray or an upper surface of the second sheet stacked on the movable stack tray; and a movable tray moving unit that moves the movable stack tray upward when the first position of the movable stack tray is lower than or equal to the predetermined first height and either the upper surface of the movable stack tray or the upper surface of the second sheet stacked on the movable stack tray is not sensed by the upper surface sensor, and does not move the movable stack tray upward when the first position of the movable stack tray is higher than the predetermined first height.