A secure link system for a quick fastening set (3, 103, 203) comprising a connection device (4, 104, 204) fastened on a tool and a coupler (5, 105, 205) which is mounted at the end of an arm of a heavy-construction machine and which is designed so as to be connected to the connection device (4, 104, 204), the secure link system (10, 110, 210) being intended to be mounted on the coupler (5, 105, 205) and to cooperate with the connection device (4, 104, 204), and comprising: - at least one locking means (13, 113, 213) biased by return means (22, 122, 222) from a disengaged position, in which, in operation, it enables the displacement of the connection device (4, 104, 204) relative to the coupler (5, 105, 205), to an engaged position, in which it is capable of cooperating with the connection device (4, 104, 204) so as to ensure retaining the tool; - at least one safety member (25, 125, 225) movable between a deactivated position, in which it does not hinder the displacement of the locking means (13, 113, 213) between its engaged and disengaged positions, and an activated position, in which it limits the displacement of the locking means (13, 113, 213) from its engaged position till an intermediate position beyond which the locking means (13, 113, 213) cannot retain the tool, in operation; - a device for releasing the tool designed to release the connection device (4, 104, 204) from the link system (10, 110, 210); characterized: - in that the link system (10, 110, 210) comprises: - return means (32, 132, 232) which bias the safety member (25, 125, 225) from its deactivated position toward its activated position; - a means (40, 140, 240) for detecting the presence of a tool, which is biased by return means (43, 143, 243) toward an armed position and which can be displaced, under the action of the connection device (4, 104, 204) during connection and against said return means (43, 143, 243), toward a unarmed position; - and in that the device for releasing the tool comprises a movable release member (45, 145, 245, 180) designed to cause, during a motion from a first position to a second position, both the displacement of the safety member (25, 125, 225) toward its deactivated position, and the displacement of the locking means (13, 113, 213) toward its disengaged position, so that, when the locking means (13, 113, 213) reaches its intermediate position, the safety member (25, 125, 225) is no longer in the activated position. - at least one locking means (13, 113, 213) biased by return means (22, 122, 222) from a disengaged position, in which, in operation, it enables the displacement of the connection device (4, 104, 204) relative to the coupler (5, 105, 205), to an engaged position, in which it is capable of cooperating with the connection device (4, 104, 204) so as to ensure retaining the tool; - at least one safety member (25, 125, 225) movable between a deactivated position, in which it does not hinder the displacement of the locking means (13, 113, 213) between its engaged and disengaged positions, and an activated position, in which it limits the displacement of the locking means (13, 113, 213) from its engaged position till an intermediate position beyond which the locking means (13, 113, 213) cannot retain the tool, in operation; - a device for releasing the tool designed to release the connection device (4, 104, 204) from the link system (10, 110, 210); - in that the link system (10, 110, 210) comprises: - return means (32, 132, 232) which bias the safety member (25, 125, 225) from its deactivated position toward its activated position; - a means (40, 140, 240) for detecting the presence of a tool, which is biased by return means (43, 143, 243) toward an armed position and which can be displaced, under the action of the connection device (4, 104, 204) during connection and against said return means (43, 143, 243), toward a unarmed position; - return means (32, 132, 232) which bias the safety member (25, 125, 225) from its deactivated position toward its activated position; - a means (40, 140, 240) for detecting the presence of a tool, which is biased by return means (43, 143, 243) toward an armed position and which can be displaced, under the action of the connection device (4, 104, 204) during connection and against said return means (43, 143, 243), toward a unarmed position; - and in that the device for releasing the tool comprises a movable release member (45, 145, 245, 180) designed to cause, during a motion from a first position to a second position, both the displacement of the safety member (25, 125, 225) toward its deactivated position, and the displacement of the locking means (13, 113, 213) toward its disengaged position, so that, when the locking means (13, 113, 213) reaches its intermediate position, the safety member (25, 125, 225) is no longer in the activated position.