A control device for an adjustable fluid jet having a piston arrangement with a through bore communicating with at least one through recess of an elastic element. A thrust bolt enters a jet tube arranged in a fixed manner at the jet head. A following control piston limits a pressure chamber supplied with the pressure medium on the other side of the thrust bolt. A sealing plug projects from the opposite end of the thrust bolt and exhibits a smaller diameter and enters in a sealing manner into an opening that departs from the pressure chamber and is supplied with the fluid to be processed.