Sheet binding apparatus, sheet processing apparatus, and image forming system

An image forming system comprising:

• an image forming apparatus including an image forming unit configured to form an image on a sheet;
• and
• a sheet binding apparatus configured to perform a binding process on a sheet on which an image is formed by the image forming unit,
• wherein the sheet binding apparatus includes:
• (A) a stapler configured to be capable of performing a binding process on a sheet bundle in a first posture and in a second posture which is different from the first posture;
• (B) a moving mechanism configured to move the stapler in a moving direction;
• and
• (C) a turn mechanism configured to turn the stapler from the first posture to the second posture in accordance with moving the stapler in the moving direction by the moving mechanism,
• wherein the turn mechanism includes:
• (1) a first protrusion and a second protrusion configured to move together with the stapler;
• (2) a first rail configured to guide the first protrusion and the second protrusion in the moving direction;
• (3) a second rail extending along an inclined direction inclined with respect to the moving direction from a downstream end of the first rail in the moving direction and configured to guide the first protrusion;
• (4) a third rail extending along the moving direction from the downstream end of the first rail and configured to guide the second protrusion;
• and (5) an introducing member having a length to introduce the first protrusion from the first rail to the second rail by coming into contact with the first protrusion, and to allow the second protrusion to enter from the first rail to the third rail,
• wherein when the first protrusion and the second protrusion are guided by the first rail, the stapler is held in the first posture,
• wherein when (1) the first protrusion is guided by the second rail and (2) the second protrusion is guided by the third rail, the stapler is held in the second posture, and
• wherein the stapler turns from the first posture to the second posture by (1) the first protrusion being introduced from the first rail to the second rail and (2) the second protrusion being guided from the first rail to the third rail, when the stapler moves in the moving direction.