PURPOSE: To prevent exfoliation of painting at the time of bending and integrally forming members by executing two painting stages; the stage of applying paintings of specific thicknesses respectively independently to the 1st member and 2nd member prior to coupling and the stage of applying finish coating after the coupling.

CONSTITUTION: A diaphragm 20 is inserted between the aperture ends of the blinded cylindrical 1st member 14 and 2nd member 18 which are constituted of sheet metals to partition the spacing between the 1st member and the 2nd member to a 1st chamber and 2nd chamber by the diaphragm 20. A spring 32 is disposed in one chamber and communicating ports 30, 32 of working fluid are provided to the 1st chamber and the 2nd chamber. The 1st member 14 and the 2nd member are respectively independently painted to about 25μm thickness and thereafter, the two members are coupled by enclosing and crimping the one flange part with the other flange part in the state of internally mounting the diaphragm and the spring therein. The communicating ports are closed and the entire surface of the two members is applied with the finish painting. The exfoliation of the paint at the time of bending the members is obviated in this way and the product having the excellent corrosion resistance is obtd.