A stapler apparatus may be provided. More specifically, a stapler apparatus capable of automatically stapling a bundle of sheets output from an image forming apparatus such as a copy machine, a printer, a facsimile or the like may be provided. The stapler includes: a guide plate in which a slot having a branch structure has been formed; a moving frame which is reciprocatively movable on the guide plate; a rotation frame which is rotatable on the moving frame and includes a plurality of levers mounted thereon, the plurality of levers moving along the inside and outside of the slot or change paths; a path change member which changes a movement path of any one of the plurality of levers; and a stapler which is mounted on the rotation frame and is in conjunction with the rotation frame.