A disposable surgical instrument includes an instrument grip forming a receiving housing. A separate handle is mounted in the instrument grip in the manner of a rocker. A shaft tool includes a shaft having at least two relatively axially movable bar or rod components and an instrument head having patient engagement elements which can be actuated by the bar or rod components, of which one bar or rod component is fixed at the proximal end thereof to the instrument grip and the other bar or rod component has an articulation point on which the handle is directly articulated in such way that a manually actuated rocker movement of the handle about the articulation point on the handle side is transformed directly into an axial movement of the other bar or rod component on the articulation point on the shaft side.