To prevent impairment of follow-up performance of expansion/contraction of a gas chamber caused by a retreat/entrance of a piston rod by forming an annular clearance between an inner periphery of a cylinder and an outer periphery of a shielding board which is sandwiched between it and a lower support board having a diameter smaller than an upper support board above an extension side damping valve and whose outer peripheral end can vertically deflect.

A vertically deflecting shielding board 13 is located above an extension side damping valve 10, and an annular clearance is arranged between this and an inner periphery of a cylinder. A jet restraining mechanism installed on the tip of a piston rod is composed of the shielding board 13 and support boards 14 and 15. At extension side operation time, a piston 3 compresses a lower oil pressure chamber A, and an operating fluid push-opens the extension side damping valve 10 through an extension side port 20 of the piston 3, and flows into an upper oil pressure chamber B. At this time, a jet restraining mechanism 12 hinders a jet, and straightens it, and sets it at proper flow speed. At compression operation time, the shielding board 13 deflects to the piston side, and a through hole 13a blocked up by the upper support board 14 is opened, and inflow resistance to a pressure side port 21 from the upper operating fluid chamber B is reduced, and a stay of the operating fluid is prevented, and an oil level is also stabilized.