PURPOSE: To obtain a weak point pin strong against fatigue and endurable for the use in a sliding part.

CONSTITUTION: A guide ring 4 is turned around by a servomotor 5, and the movement is transmitted to a guide vane 1 through a link 3 and an arm 2 for opening and closing the guide vane 1. A weak point pin 11 provided in the connecting part between the above-said link 3 and arm 2 is made of aluminium alloy to be larger in the outer diameter of its breaking part than the former one made of steel by the reduced shearing stress. Besides, it is given hard chromium plating 12 in its sliding part on the outside, and is harder in its surface of the sliding part than the former one made of steel to be sufficiently available for a sliding part.