PURPOSE: To enlarge application by providing two connecting ports communicated with an external liquid pressure passage via a first cylinder barrel provided with two liquid passages communicated with a first and a second common liquid passages and also via a rotary joint.

CONSTITUTION: A fluid discharged from a second cylinder 13 in its forward stroke is sucked into a first cylinder in its backward stroke through a second cylinder port 30, the outer chamber of a cavity 61 and a first cylinder port 21. In a case of providing input from a second shaft 2 and fetching output from a first shaft 1, the torque outputted from the first shaft 1 and the rotating speed can be controlled by connecting the output shaft of a hydraulic motor 81 to the first shaft 1 by gears or the like so as to make addition to the capacity of the hydraulic motor 81 formed of a first cylinder barrel and the like or performing cut-off by the operation of a change-over valve 80 connected to outside connecting hydraulic ports 76, 77. This results in enlarging application fit for many uses by changing these external apparatus.