A device for varying the pitch of the propeller blades in an engine driven boat. A hydraulic motor having a work cylinder with a working piston imparts movements to the propeller blades and to an auxiliary cylinder through a mechanical transmission member. The auxiliary cylinder includes a follow-up slide which cooperates with the transmission member. The transmission member has inlet and outlet openings and a channel to conduct a pressure medium to and from the working cylinder. The follow-up slide has inlet and outlet openings which cooperate with the openings in the transmission member so that control of the position of the working piston is determined by the position of the follow-up slide.