Abstract: A device for arresting the fall of a climber ascending or descending along a vertically disposed rail, such as a guide rail secured to a ladder, including a support member having an opening therein for receiving the rail therethrough, a clamping member supported on the support member and engageable with a vertical surface of the rail in clamping relation therewith, at least one connecting link pivotally connected to the support member, and an actuating lever pivotally connected to the connecting link, the actuating lever having one end thereof engageable with the clamping member and an opposite end thereof connectable to the climber where upon a sudden downward movement of the climber, as when the climber may be caused to fall, the connecting end of the actuating lever shall be caused to pivot downwardly, forcing the clamping member and the support member into clamping engagement with the rail, thereby arresting the fall of the climber.