To provide a technology of preventing an optical signal from being mistakenly recognized as an optical noise even when a surge occurs. A control device of a node that transfers signal light monitors inputted light, determines, when power of the inputted light reaches a saturation level of a monitor unit as a result of monitoring, that the inputted light is signal light, further determines based on a spectral line shape of the inputted light, when the power thereof does not reach the saturation level, whether the inputted light is the signal light or ASE light; and stops a transfer of the ASE light if determined to be the ASE light.