To provide a protection function, economize nodes and improve flexibility on a network construction.

Parent node combines two or more wavelengths of sending light signals at one port. Wavelength combining/dividing element 213 to divide a receiving light signal input on one port into two more wavelengths, and light switch 211 to switch connection between ports for active system and for the above mentioned standby system are provided. The child node is connected to light transmitting paths for the active system and the standby system, respectively. WDM splitter 204 combines/divides light signals of wavelengths distributed to each child node. Light splitter 233 to combine two ports for the active system and the standby system at one port, and WDM splitter 231 to combines/divides sending light signal and receiving light signal input at one port into two ports are provided.