Abstract: Provided is a stapler device installed to staple a bundle of papers processed and discharged from an image forming apparatus or a post-processing apparatus. The stapler device includes a stapler, and a moving unit installed to allow the stapler to reciprocate in a direction intersecting with a discharge direction of the bundle of papers. The moving unit may rotate the stapler outwardly such that a bundle of papers inserted from the outside in addition to the discharged bundle of papers is stapled in at least one end position of a range of the reciprocating movement.