PURPOSE: To prevent an abrupt idle turning of a guide vane by providing a plastically deformable arm whose one end is secured to the guide vane and the other is to a link with a fragile pin so as to be deformed when the fragile pin is broken off.

CONSTITUTION: In case a fragile part 6a of a fragile pin 6 is broken off because a guide vane 1 might seizure on foreign matters while it makes a closing motion or the fragile pin 6 or it is broken down due to its fatigue, the guide vane 1 provides some linkage means with a servo motor 9 by means of a plastically deformable arm 10 so that the guide vane does not get free. Said arm 10 is designed so as to make a sufficient plastic deformation against a moment of opening or closing the guide vane 1, thereby preventing a separation of a guide vane arm 4 and a link 7 as well as an abrupt idle revolution of the guide vane 1.