PURPOSE: To make the decceleration and stopping positions of a piston adjustable by inserting a movable ring having a central hole and a throttle hole in a cylinder tube, and movably and adjustably installing a magnetic attraction member outside the cylinder tube.

CONSTITUTION: A movable ring 20 having a central hole 21 and a small-diameter throttle hole 23 is inserted in a cylinder tube 1 made of non-magnetic material. A permanent magnet 25 is movably installed on the outer periphery of the cylinder tube 1 by means of a screw bar 30. Consequently, when the screw bar 30 rotates to move the permanent magnet 25, the movable ring 20 moves to a specified position, so that it is possible to optionally adjust positions where the decceleration of a piston 2 is started and the piston 2 is stopped.