PURPOSE: To realize smoother sliding guide by improving a sliding guide structure of a force releasing member covering an interlocking body in a structure wherein a slit is formed in one side of a cylinder pipe and the interlocking body is connected to a piston via a connecting means through the slit.

CONSTITUTION: A cylinder pipe 1 with a piston 3 mounted therein is shaped to a configuration having a substantially square cross section. A slit 10 extending in parallel with a cylinder axis is formed in one wall 8 of the cylinder pipe 1. An interlocking body 17 is connected to the piston 3 via a web-like connecting means 16 passing through the slip 10. The interlocking body 17 is covered by a U-shaped force releasing member 18, and the member 18 is freely guided in the axial direction along the cylinder pipe 1 by a guide device. Further, the slit 10 is fluid-tightly covered with a seal belt 19 inside the cylinder pipe and simultaneously covered with a cover belt 21 outside the cylinder pipe. The guide device is composed of guide pieces 35, 36 along guide tracks formed on both sides of the slit 10, and the like.