The invention relates to an optical fiber sealing unit that contains a basic bundle consisting of light-transmitting fibers, a signalling bundle also consisting of light-transmitting fibers, a cable sheath, and receiving bodies positioned at both ends of the cable sheath. The receiving bodies have an accepting space suitable for the fixing of at least some of the light-transmitting fibers, and a transmitting body that allows light to pass through it. The basic bundle and the signalling bundle are arranged in the cable sheath, and the one end and the other end of the basic bundle are each fixed in the accepting space of a receiving body in such a way that they cannot move, one end of the basic bundle being fitted to the transmitting body of one of the receiving bodies, and the other end of the basic bundle being fitted to the transmitting body of the other receiving body. One end of the signalling bundle is fixed in the vicinity of the one end of the basic bundle so as to prevent light input, while the other end of the signalling bundle is clamped into the light-transmitting output member in the vicinity of the other end of the basic bundle.