To prevent operation errors in the setting work when installing a master unit and a slave unit and simplify the setting work by autonomously setting information relating to the master unit and the slave unit of an optical transmission device.

On receipt of a request for reading out configuration information from a remote monitoring device 9, the connection state of the slave unit 2 is notified to the remote monitoring device 9 from the master unit 3 and the slave unit 2 of the optical transmission device. On receipt of a request for canceling the ALM mask from the remote monitoring device 9, an alarm mask is canceled for all the slave units 2 directly connected or indirectly connected in series to the master unit 3. On receipt of a request for setting the ALM mask from the remote monitoring device 9, an alarm mask is set up for the slave unit 2 connected to the farthest end of the master unit 3. On receipt of a request for setting information relating to various devices from the remote monitoring device 9, predetermined device-related information is set for all the slave units 2 directly connected to the master unit 3 or indirectly connected in series to the master unit 3.