On an outside of a damper main body, there is provided a case which is movable up and down and which is connected to a damper rod. Between the damper main body and the case, there is formed a pressure chamber which is filled with a pressure medium which changes its state between a gaseous state and a liquid state. A heating chamber to flow therethrough a heating medium which is heated by the heat of the driving source or the like of a vehicle is disposed in a manner to contact a liquid sump portion of the pressure chamber. The pressure medium is heated and evaporated by the heat of the heating medium to thereby increase the internal pressure of the pressure chamber. The case is thus pushed upward and the damper rod is moved up, whereby the vehicle height increases.