Provided is a group subordinate terminal in a key updating system that includes a server and a group of terminals including: a group managing terminal; and group subordinate terminals including the group subordinate terminal, the group subordinate terminal comprising: a group withdrawal request processing unit which transmits a group withdrawal request to the group managing terminal in response to an instruction to update its apparatus-unique key, the group withdrawal request requesting for withdrawal of the group subordinate terminal from the group; an update apparatus-unique key requesting unit which requests for another apparatus-unique key by transmitting to the server a group withdrawal certificate indicating that the withdrawal of the group subordinate terminal from the group of terminals is completed through invalidation of its group key; and an update processing unit which updates the apparatus-unique key held in an apparatus-unique key holding unit to the another apparatus-unique key obtained from the server.