A hydraulic swash block positioning system for positioning a swash block to set a variable displacement, the hydraulic device including a rotor with pistons and piston chambers, the positioning system having, between the housing and the swash block, a positioning cylinder with a positioning piston forming a positioning chamber for setting an average value of the swash block position and a control valve connecting the high oil pressure source with the positioning chamber through a feeding line. In accordance with the invention the feeding line is connected to an oil container that has a variable container volume that can be adjusted synchronously with the changes in the number of piston chambers connected to the high oil pressure source.