When a discharge count has exceeded a specified number of sheets, a sheet discharge device executes a process of moving down a discharge tray by a specified quantity and thereafter moving up the discharge tray until a top-surface detection part outputs a top-surface detection signal, while clocking a move-up time lasting from a move-up start of the discharge tray until output of the top-surface detection signal by the top-surface detection part. When the move-up time is equal to or less than a reference time, the sheet discharge device makes a next sheet discharged while the top-surface detection part outputs the top-surface detection signal; on the other hand, when the move-up time is more than the reference time, the sheet discharge device executes a correction process of moving down the discharge tray before making the next sheet discharged.