The folding device includes a folding unit and a prior moving unit. The folding unit performs the folding process on the paper aligned by the alignment member positioned at the folding position. The prior moving unit moves the alignment member from the folding position to the home position or the alignment position according to a position of the end of the paper being moved in the folding process. This can put ahead the starting time for moving the alignment members and reduce the time required for a subsequent folding process, thereby improving efficiency (productivity) of the folding process as a whole.