To provide a paper sheet processing device which folds a paper sheet at a desired position while suppressing faulty conveyance, and to provide an image forming apparatus.

The paper sheet processing device includes: a pair of plate-like members, at least one of which is movable; a moving means which moves the movable plate-like member; a paper sheet arranging member which arranges the paper sheet while coming into contact with the leading edge of the paper sheet; roller pairs which can be displaced between a paper sheet holding position and a retreating position; a pushing member which pushes the paper sheet into a paper sheet folding part; and a paper sheet folding unit which holds the paper sheet in between and folds the paper sheet. The paper sheet processing device has a control unit which performs such control that: the movable plate-like member is moved by the moving means so that a space between the pair of plate-like members may be narrowed, the paper sheet is conveyed to the pair of plate-like members, the paper sheet arranged by making its leading edge abut on the paper sheet arranging member is held between the pair of plate-like members, and the roller pairs are displaced to the holding position and hold the paper, and then the movable plate-like member is moved by the moving means so that the space between the pair of plate-like members may be widened, to cancel holding of the paper between the pair of plate-like members.