A metallic protecting cover is formed from two axially split members, i.e. a first protecting cover member secured to a mounting eye, and a second protecting cover member having an overall length shorter than that of each of first and second cylinders and having a predetermined gap between itself and the second cylinder. The second protecting cover member is press-fitted into the first protecting cover member secured to the mounting eye to integrate the first and second protecting cover members into the protecting cover. Accordingly, the lower end of the second cylinder can be caulked in a state where the second protecting cover member has been temporarily assembled to the second cylinder. Thus, it is possible to ensure the required strength of the protecting cover and to increase the degree of freedom in assembly process.