A communication network system includes a cloud server device connectable with an external device via a global network, and a gateway device. The gateway device includes a first communication section which communicates with the cloud server device via the global network; a second communication section which communicates with an internal device via a local area network; first and second communication controlling sections which respectively control the first and second communication sections; and a communication history storage section. After establishment of a session between the external device and the internal device under the control of the first and second communication sections by the first and second communication controlling sections, the communication history storage section stores communication history information about a history of the communication between the external device and the internal device.