Abstract: Safety device for working at great heights, comprising a cable (2) stretched parallel to a direction of movement and carried by spaced supports (4), and a hooking element (33) sliding along the cable. Each support consists of a substantially horizontal axle fixed at one end on a fixed part (41) and carrying at its other end a plate (5) holding the cable (2). The plate is mounted for rotation on the axle (40) and has two opposite notches (51) in which the hooking element engages by sliding on the cable (2) in order to pass above the support axle (40) through rotation of the holding plate (5), the latter being automatically returned to a rest position in which the two notches (51) are aligned with the cable (2), each in one direction.