The line jammer device is a device for jamming a line which is under tension upstream of the device when it is in a locked state and releasing the line when it is in an unlocked state. The device has a first line gripping member and a second line gripping member. The first line gripping member has a circular surface around which the line is wound between a fraction of a turn corresponding to an angle of more than 180.degree. and at least one turn. The second line gripping member is arranged in such a way that the grip it exerts on the line is exerted once the line has been wrapped around the first gripping member between a fraction of a turn corresponding to an angle of at least 180.degree. and at least one turn.