Junction device, and undersea cable system

A branching device inserted into a transmission path and a power supply path connecting a first trunk station and a second trunk station, the branching device comprising:

• a branching unit that is connected to a branch station by a transmission path and a power supply path, and switches a route by controlling a switch inserted into the transmission path and the power supply path;
• and
• a reconfigurable optical add/drop multiplexer (ROADM) device that is inserted into a transmission path and a power supply path connecting the branch station and the branching unit, and supplies, to the branching unit, a control signal for controlling the switch of the branching unit, wherein
• the branching device further comprises
• a current detection unit for detecting that there is no current flowing through a power supply path between the branch station and the branching unit,
• a first optical signal detection unit for detecting an optical signal in a transmission path connecting the branch station and the branching unit, and
• a switching unit for controlling the switch in such a way as to connect a transmission path between either of the first trunk station and the second trunk station, and the branch station, when the current detection unit detects that there is no current flowing through a power supply path between the branch station and the branching unit, and the first optical signal detection unit detects an optical signal in a transmission path connecting the branch station and the branching unit.