PURPOSE: To synchronize each mechanism of piston cylinders accurately and to improve machining accuracy by a method wherein by the working liquid discharged when a piston cylinder mechanism on the front stage side is set into motion, the piston cylinder mechanism on the next stage side is operated.

CONSTITUTION: When the exhaust port of a pump P1 is connected with a pipe L1, the liquid in a liquid chamber 150 flows into a cylinder 11a at the lower part of a left piston 13 through a pipe L1 and lifts the piston 13. At this time, the liquid in the cylinder 11a on the upper side of the piston 13 flows from a working passage b into a cylinder 21a at the lower part of a right piston 23 through a working passage c and a pipe L3. By this a piston 23 and piston rods 24a, 24b are moved upward at the same stroke as those on the left side. By the upward movement of these right and left piston rods 14a, 24a, a movable arm 7, a tool rest 8 and a tool 9 fixed on these rods are moved upward simultaneously and the tool 9 separates upward from a collet chuck 3. Hereafter, a work 100 is held by claws 312.