<p>A sheet binding (1) apparatus includes a support (9) for supporting a set of sheets (2); a puncher (3) for punching the sets of sheets (2) on the support; binder (7) for binding the sheets by penetrating a ring member (6) through punched holes of the sheets punched by the puncher (3); a detector (60) for detecting a size of the ring member (6) supported on the binder (7); a changing device for changing a degree of opening of the ring member (6) in accordance with a size of the ring member (6); a conveyer (5) for conveying the set of sheets (2) punched by the puncher (3) to the ring member (6) supported on the binder (7); a second support for supporting the binder (7) for movement between an automatic mode position wherein the binder (7) receives the set of sheets (2) conveyed by the conveyer (5) and a manual mode position wherein the set of sheets (2) can be received without use of the conveyer (5); a second detector for detecting the manual mode position of the binder (7) and for prohibiting conveyance of the sheets by the conveyer (5); ring controller for controlling the degree of opening of the ring member (6) during the manual mode; wherein the ring controller opens the ring member (6) to the degree of opening predetermined in accordance with the size of the ring member (6).</p>
