When a sheet is conveyed to a position where a conveying speed can be changed from a first conveying speed to a second conveying speed while a discharging unit is discharging a preceding stack of sheets, a conveyance control unit calculates a third conveying speed for conveying the sheet based on a first conveyance time to be taken until a leading end of the stack of sheets reaches a second tray unit from a first tray unit and a second conveyance time to be taken until a current discharging operation is completed from a start of the current discharging operation, and changes the conveying speed from the first conveying speed to the third conveying speed.