To predict the latest location of a partner and to narrow down a range for finding the partner even in case of a failure in making contact with the partner through a cellular phone etc.

A management server receives a first ID, an ID reader identifier, and a check time in time series from an ID reader group having communicated with a first ID tag among a plurality of ID readers, and stores them in time series in an ID reader check list table. A user terminal transmits a retrieval request including the first ID to the management server, which reads out an ID reader identifier of an ID reader group, corresponding to the first ID included in the retrieval request, among ID reader identifiers stored in the ID reader check list table, and the check time. The management server reads out an ID reader installation place name group, corresponding to the ID reader identifier of the ID reader group, among ID reader installation place names stored in an ID reader installation place table, and transmits a retrieval result, showing the first ID, ID reader installation place name group, and check time in time series, to the user terminal.