In a premises gateway device that performs encryption or decryption under the IPsec, the throughput of a processor is varied depending on a type of data to be treated in order to realize reduction in power consumption. In the premises gateway device to which a telephone, PCs, and a home appliance that are pieces of home network equipment are connected and which transmits or receives data using an ISP and an IPsec tunnel via an ONU, an OLT, and a carrier network, relevant home network equipment and a data rate are decided based on the data to be treated. The frequency of a clock to be fed to the processor is varied depending on the information.