To make efficient use of a bandwidth per optical communication path in an optical wavelength division multiplex transmission network.

A transmission device 1A transmits data input from a client device 2 to a transmission device 1B through an optical wavelength path 10. A monitoring control device 4 stops an output of the optical wavelength path 10 when the amount of traffic communicated on the optical wavelength path 10 is less than a predetermined value and notifies a monitoring control device 3 of the stop. A management control device 3 notifies the transmission device 1B of stopping the optical wavelength path 10, and the transmission device 1B stops an output of the optical wavelength path 10. The monitoring control device 4 notifies the management control device 3 of a resumption request when the traffic amount exceeds a predetermined value, and the management control device 3 allocates a non-operating optical wavelength path 10 and notifies transmission devices 1A and 1B of start permission. Each monitoring control device 4 starts implementing communication through the allocated optical wavelength path 10 and notifies the management control device 3 of resuming the optical wavelength path 10.