PURPOSE: To prevent an elastic body located between a case cover and a stopper from being cracked by making an abutting surface of each upper and lower stopper, which abuts against a car body side when a piston rod moves up and down exceeding a preset limit, to be formed in an arc in its section.

CONSTITUTION: Abutting surfaces of upper and lower stoppers 7a and 7b, which abut against a car body 4 side when a piston rod 6 moves vertically exceeding a limit, are covered with elastic bodies 10 and 11, while the sectional form of the abutting surfaces is formed into an arc, and the stoppers 7a and 7b are installed at a core member 7 attached to a tip of a rod 6. When amplitude of vertical outer force via the rod 6 is large, the stoppers 7a and 7b become in abutment with an insulation case 2 or a case cover 3 through the elastic bodies 10 and 11, and this deforms the elastic bodies 10 and 11. However, since the force of the stoppers 7a and 7b compressing elastic bodies 10 and 11 over the surfaces of the stoppers 7a and 7b, whose sectional from is of an arc, the elastic bodies 10 and 11 are free of cracks.