System, method and program for monitoring

Provided is a highly reliable light node system capable of monitoring an optical path in a transmission node and a transponder in a node under the working conditions thereof. The light node system includes: a monitoring control managing means by which to monitor an inspection signal or an operation signal connected to at least one of the ports of a wavelength selection switch; and a control means for controlling the wavelength selection switch so that the monitoring control managing means can carry out monitoring.