A binding mechanism cartridge is detachably held by a binding device body instead of a staple cartridge which is detachable into the binding device body. The binding mechanism cartridge includes a body portion, an upward-and-downward moving portion and a base portion. The body portion is detachably held by the binding device body. The upward-and-downward moving portion is on the body portion to move close to or away from one surface of a bundle of sheets by moving upward and downward by interlocking with a drive mechanism of the binding device body. The base portion is on the body portion to face the upward-and-downward moving portion and supports the other surface of the bundle of sheets. The upward-and-downward moving portion includes a binding mechanism which is partially in pressure contact with the one surface according to a movement of the upward-and-downward moving portion to binds the bundle of sheets.