PURPOSE: To make a space for providing a servomotor unnecessary by a method wherein an outside ring is slid into the circumferential direction thereof by supplying pressure oil and the lower stage guide vane is driven to open and close it by a link mechanism.

CONSTITUTION: The pressure oil is supplied into a space through a tube for opening the guide vane among pressure oil flowing tubes 22 while the pressure oil in a pressure chamber 31 is discharged from the tube 22A for closing the guide vane. According to this operation, the outside ring 21 is slided into the circumferential direction thereof and the lower stage guide vane 6 may be opened through the link mechanism 26. When the supplying direction of the pressure oil is reversed, the lower stage guide vane 6 may be driven into the direction of closing. Accordingly, the provision of the special space for providing the servomotor is made not necessary and the size of a lower chamber assembly may be reduced.