PURPOSE: To easily fit a moving member for adjusting car height to the external surface of a cylinder, reduce the number of components, improve assembly, and reduce cost by providing two step sections or more on the external surface of the cylinder.

CONSTITUTION: Two step sections 35 and 25 are provided on the external surface of a cylinder 16 so that the head side can sequentially be diametrically extended and a moving member 26 with an internal surface that is equal to the maximum diameter circumference is externally engaged in the cylinder 16 from the intermediate large diameter section of the cylinder 16. The right of the moving member 26 is formed in a spring catch shape and formes a pressure room 28 between the member and the cylinder 16. The pressure room 28 is connected to a sub-tank through an oil path 29 perforated in the moving member 26. When car height is increased, pressure oil is introduced into the pressure room 28 and the moving member 26 is moved right and the counter-force of a coil spring is increased. When the car height is decreased, the pressure oil of the pressure room 28 is discharged to the sub-tank.