PURPOSE: To enable electrification without necessitating large operation lever by constituting a valve by a rotary valve in a gas spring which is provided with a valve which can connect or shut off first and second pressure chambers.
CONSTITUTION: When the length of a gas spring is adjusted, a switch 17 is first turned on, an output shaft 16A of a motor 16 is turned by 180, and a valve rotor 22 is set to the illustrated condition. A first pressure chamber P 1 is connected with a second pressure chamber P 2 via a knotched section 5A which is formed in a circular member 5, a passage chamber Po between an inner cylinder 1 and an outer cylinder 4, a connecting passage 7C of a valve body 7, and a hole 22B in the direction of diameter and an inner hole 22A of a valve rotor 22. When elongation action is done in this connecting condition, external force which acts on the gas spring is removed. Then, gas flows from the first pressure chamber P 1 into the second pressure chamber P 2 via a connecting passage 14, and a piston rod 3 starts to elongate. That is, the outer cylinder 4 is guided by a guide cylinder 8 and rises.