Abstract: A guide vane protecting device for use in a hydraulic turbine. The device has a braking system having a first and a second braking members by which an initial braking power is imparted to a first control member interposed therebetween. The braking system further has a translational sliding mechanism which permits the translational sliding movement of the first braking member onto the first control member so so to cause a uniform increase of the braking force exerted by the braking members on the first control member, when a weakened pin incorporated in the protecting device is broken by an extraordinary force caused by, for example, jamming of foreign matter between adjacent guide vanes.