CUSTOMER PREMISES OPTICAL NETWORK UNIT

There is provided a customer premises optical network unit (ONU) capable of reading management signals and of outputting data through an external node by using I2C serial interfaces. In the ONU, an ONU functioning section has another serial signal terminal and is connected with a first management processing section through a sub-serial transmission path. The first management processing section is also connected with a MSA interface module through an additional monitoring signal transmission path and a monitoring signal transmission path. The monitoring signal transmission path on the side of the MSA interface module is connected with a sub-I/F section. A part of management signals set in an OAM layer of a signal transmitted between an OLT and the ONU may be outputted to an external node by using the first management processing section, the additional monitoring signal transmission path and the monitoring signal transmission path.