An object of the present invention is to ensure rigid formation of the folds of the protrusions of the paper sheet and smooth conveyance of the folding-processed paper sheet to the downstream side of the folding position in the paper conveyance direction without causing the problems such as jamming. A folding unit includes a lower guide plate arranged at a position facing a folding plate at the folding position, and an arrangement position of a turning shaft of the folding plate is vertically movable with respect to the lower guide plate.