The invention relates to an instrument (30) with an elongated first shaft (42), an end effector which is arranged on a distal end of the first shaft (42) and an actuation unit (19) arranged on the proximal end of the first shaft, wherein the actuation unit (19) comprises a first wheel (32) which is connected non-rotatably with the first shaft (42). The first shaft (42) is axially displaceable in relation to the first wheel (32) and is in threaded engagement with a second wheel (33) which is axially immovable in relation to the first wheel (32).