PURPOSE: To prevent abnormal sound from being generated, by generating damping force at both of an extension stroke and a contraction stroke by means of one damping force generation mechanism built in a piston, and setting free the inflow of operation oil into an extending chamber.

CONSTITUTION: A check valve 4 is closed due to pressure rise in an upper chamber 3a at the time of an extension stroke, and operation oil in the upper chamber 3a flows from passages 1d and an opening 6e to a middle chamber 3b, and pressure difference is generated by means of a damping force generation mechanism 6, and operation oil flows from oil discharge holes 3d to a reserver chamber 12. The capacity of a lower chamber 3c is enlarged, but due to circulation being free from passages 10a, 10b at a bottom cap 10 to the lower chamber 3c, operation oil is supplied from the reserver chamber 12, and the pressure of the lower chamber 3c is not reduced. At the time of a contraction stroke, a check valve 13 is closed due to the ascent of the lower chamber 3c pressure, and the check valve 4 is opened, and operation oil flows from passages 1c to the upper chamber 3a, but its flow is smaller than flow from the lower chamber 3c to the upper chamber 3a, so the pressure of the upper chamber 3a ascends in the same way as that of the lower chamber 3c. Accordingly, the generation of abnormal sound due to cavitation/aeration can be prevented.