Extended terminal device, aggregation device, communication system, communication method, and communication program

An extended terminal device (4) according to the present disclosure comprises: a first communication unit (41) that uses a first communication method to communicate with at least a portion of a plurality of terminal devices; a second communication unit (42) that performs communication by using a second communication method different from the first communication method; a multi-hop communication control unit (44) that performs control of multi-hop communication in a multi-hop network where an aggregation device serves as a master station; and a protocol conversion processing unit (43) that performs protocol conversion of uplink data from the first communication method to the second communication method when the first communication unit (41) receives the uplink data, which is data to be sent to the aggregation device and is for managing the terminal device, from the terminal device. The second communication unit (42) transmits, to a counterpart device that is a next node on an uplink path to an aggregation devi