Binding apparatus, paper processing apparatus and image forming system

In a binding apparatus having a pair of guide shafts (200a, 200b) fixed respectively to a front side plate and a rear side plate by a corresponding screw and a pair of stays (204, 205) fixed between the front and rear side plates, a stitcher (5a) and a clincher (5b) are movably supported in the longitudinal direction on the guide shafts (200a, 200b), wherein a binding section (T) for binding a paper sheet bundle is interposed between the stitcher (5a) and clincher (5b). The stitcher (5a) and clincher (5b) are arranged in such a way that a staple needle in the stitcher (5a) is movable along the center line (M) connecting the centers of the guide shafts (200a, 200b) to each other.