To automatically secure the effective engagement length of a screw joint portion using mechanical locking means without visibly checking a marking of the effective engagement length of the screw joint portion between an outer shell and an extension bracket in a hydraulic shock absorber.

The extension bracket 6 having a play portion 13 on the bottom side in the range of the mounting adjustment length of the hydraulic shock absorber 1 is threadedly inserted into a base end outer periphery portion of the outer shell 2 with a male screw 5 engraved in the outer periphery face, through a female screw 14. A fitting hole 12 and a through-hole 15 adaptable to the side faces of the outer shell 2 and the extension bracket 6, respectively, are provided in such a range that the effective engagement lengths of the male screw 5 and the female screw 14 do not exceed design strength with both relative rotation. A spring ring 17 is wound on the outer periphery face of the extension bracket 6 with its one end insertable from the through-hole 15 of the extension bracket 6 to the fitting hole 12 of the outer shell 2 with spring force. In this condition, the mounting length of the hydraulic shock absorber 1 can be adjusted while restricting the effective engagement length of the male screw 5 of the outer shell 2 and the female screw 14 of the extension bracket 6 is restricted not to exceed the design strength.