Abstract: A stapler (1) for stapling together a workpiece (7), primarily a sheaf of papers, in which the stapler comprises a stapling unit (3) and an anvil (2), which interacts with the stapling unit and on which the workpiece is placed, and against which stapling is performed, which stapling unit and an anvil are, by means of a drive means (4), driven relative to each other in a reciprocating stapling movement (P), during which movement stapling takes place, wherein the stapling unit comprises a frame (8) and a staple cassette (9) which houses staple blanks (32) and which is exchangeable, and which is detachably connected to the frame by attachment devices (10), wherein the staple blanks are fed one by one to an outlet channel (56) by a feeding device (13) incorporated in the stapler, through which outlet channel a staple (35) which has been fed and formed into staple shape during the stapling movement is driven, by a blade-shaped driver (45) incorporated in the stapler, to staple the workpiece, which driver is driven