Sheet post-processing device and image forming system

A sheet post-processing device, comprising:

• a processing tray disposed inside a device main body, so that a sheet is loaded on the processing tray;
• a post-processing section that performs predetermined post-processing on the sheet loaded on the processing tray;
• a discharge outlet through which the sheet on the processing tray is discharged;
• a discharge tray disposed movably along a side face of the device main body extending downward below the discharge outlet, so that the sheet discharged through the discharge outlet is loaded on the discharge tray;
• a discharging member that conveys the sheet on the processing tray toward the discharge outlet, and discharges the sheet onto the discharge tray through the discharge outlet;
• a lifting mechanism that drives the discharge tray to move in an up and down direction;
• and
• a control unit that controls the movement of the discharge tray in the up and down direction driven by the lifting mechanism, wherein
• when discharging the sheet onto the discharge tray, the control unit sets position of the discharge tray in the up and down direction to a predetermined discharge position, and
• when loading the sheet onto the processing tray, the control unit sets the position of the discharge tray in the up and down direction to a loading position lower than the discharge position.