A sheet processing apparatus includes a curling unit which curls an end portion of a sheet, and a folding device which is disposed downstream of the curling unit and folds a sheet or a sheet bundle curled by the curling unit. In one embodiment, the bow sight includes a frame having an upper portion and a lower portion that cooperate to define a target viewing opening, the lower portion of the frame including a sight pin support that is pivotally movable relative to the upper portion of the frame. The intermediate portion of the exterior envelope has a capacity for elastic deformation in the longitudinal direction, for example by virtue of oblique openings.