Monitoring equipment for optical digital communications

The object of the present invention is to realize monitoring equipment for optical digital communications which can measure the quality of or acquire data in communication networks without reducing the optical power in communication networks. In the monitoring equipment for optical digital communications which measures the quality of optical digital communication networks to which a plurality of network equipment is connected, the present invention is characterized by having at least one O/E converter that converts optical signals transmitted in an optical digital communication network to electrical signals and at least one E/O converter that converts electrical signals from this O/E converter to optical signals and outputs them to the optical digital communication network and by implementing quality measurement using the output of the above O/E converter.