The invention relates to a belayer/descender safety device (1), cooperating with a rope (2), comprising means (5) to hold said rope (2) and rotationally fixed to a chassis (6) on which enclosure means (10) for said rope (2) are mounted with pivoting and cooperating with said holding means (5). The enclosure means (10) and the chassis (6) comprise a housing (12) in opposition in the locking position which cooperates with a hook means, in particular, a spring hook, wherein said holding means (5) has the form of a pulley housing means for regulation of the speed of rotation thereof.