An object of the present disclosure is to enable an ONU to acquire ID information of terminal devices even when a network device is connected between the ONU and the terminal devices, and to thereby enable generation of a logical path between the ONU and the OLT. The present disclosure relates to an optical communication network system configured to connect terminal devices and a passive optical network (PON) system via a network device. The PON system includes an optical line terminal and an optical network unit connected using an optical transmission line. The optical network unit is configured to construct a tunnel to the network device, acquire ID information of the terminal devices connected to the network device from the terminal devices via the tunnel, and generates a logical path to the optical line terminal on the optical transmission line using the acquired ID information.