A surgical instrument includes an end effector, a manipulation unit, a grip detecting unit, a driving unit, and a control unit. When the control unit determines that the end effector is applying the acting force to the target based on the information acquired by the grip detecting unit, the control unit sets an acting force increasing zone of a predetermined range in a first movable range in the first direction of the manipulation unit, sets a neutral zone in a remaining area of the first movable range, controls the driving unit so that the acting force increases with a constant gradient with respect to an amount of manipulation of the manipulation unit in the acting force increasing zone, and controls the driving unit so that the acting force is kept constant regardless of the amount of manipulation of the manipulation unit in the neutral zone.