PURPOSE:To achieve the simplification, miniaturization and low-cost in a device by making the vibration damping force itself of a shock absorber the power source for adjusting ground clearances, and making it possible to adjust ground clearances so as to be a low ground clearance when the vibration damping force is small, and to be a high ground clearance when this is large. CONSTITUTION:In a twin-tube type shock absorber 1 which is made up of a piston 5 fitted in a cylinder 2, a cylinder member 10 is fixed on the upper part of a rod 4 being integral with a piston 5, and therein a cylinder member 11 being slidable in the axial direction along the rod 4 is fitted to constitute a hydraulic cylinder device 9. The cylinder chamber E of the hydraulic cylinder device 9 is communicated with the upper and lower chambers A, B through an oil passage 16, formed in the rod 4, in which a check valve 19 with an orifice which opens when the oil pressure inside the upper or lower chamber A or B exceed a prescribed value is interposed. Further, in the communicating part of this oil passage 16 to the lower chamber B, a valve 17 which is closed when the oil pressure in the upper chamber A becomes greater than a prescribed value is provided.
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