PURPOSE: To improve stop position setting accuracy and the duration of life by connecting a cam shaft, rotated by the movement of a slide shaft connected to a piston rod, to the feedback shaft of a servo valve, and providing a variable throttle part at the return oil passage of the servo valve.

CONSTITUTION: Inside a slide shaft 70 moved together with the piston rod 31 of a hydraulic cylinder 32, a cam shaft 71 rotated by the movement of the slide shaft 70 is provided, and this rotation is transmitted to the feedback shaft 42 of a servo valve 37 through gears 77, 78. The feedback shaft 42 is provided with a first to a third ports 57-59 connected to the ports a, b of the hydraulic cylinder 32 and a tank, as well as with an input shaft 43 rotatable therein. The input shaft 43 is provided with a pressure passage 62 and a return groove 64 so that the opening area between the return groove 64 and the third port 59 is changed by the relative rotation between the input shaft 43 and the feedback shaft 42. Stop position setting accuracy and the duration of life are thereby improved, and control time can be shortened.