To provide an slack storage unit capable of easily and safely processing the slack of a communication line.

The slack storage unit 5 is disposed in a stage adjacent to a communication unit 4, includes a protrusion 10 fittable to the outgoing line opening 11 of the communication unit 4, and is linked with the sliding operation of the communication unit 4. Also, a freely stretchable and bendable flexible duct 12 is attached to the slack storage unit 5, and the communication line made to come out from the communication unit 4 is stored inside the flexible duct 12 on the slack storage unit 5 through the outgoing line opening 11 provided in the communication unit 4.