Stapler (1) for driving staples (4) into a workpiece (6), comprising a body (2), an elastic member (7) connected to a driver (9) and an articulated arrangement (12) for tensioning of the member (7) comprising a lever (13) with a long arm (15) and a short arm (16) coupled rotatably to the body by a first coupling shaft (14), an articulated arm (17) coupled rotatably to the body by a second coupling shaft (18) and connected to the member (7) in a force-influencing manner, an intermediate joint (19) with a third coupling shaft (20) assigned rotatably to the short arm (16) at a first distance (a) from the first coupling shaft and assigned rotatably to the articulated arm (17) with a fourth coupling shaft (21) at a second distance (b) from the third coupling shaft (20), the first distance has the distance line (a) and the second distance has the distance line (β), which form the angle (γ) between themselves, the member (7) is tensioned in that the lever (13) is rotated (N) about coupling shaft (14) from a starting position to an end position, due to which the lever via the intermediate joint causes the articulated arm to rotate (R) about the coupling shaft and tension the member (7) by guiding this from a first neutral untensioned position to a second tensioned position, wherein the first distance (a) is 1.2-1.6 times greater than the second distance (b).