At the time when generating a secret key of each entity by using each divided identification information (ID division vector) obtained by dividing identification information (ID vector) of each entity into a plurality of blocks and by using a secret symmetric matrix of each key generating agency (center), a part of the components of the symmetric matrix is extracted in accordance with each divided identification information (ID division vector) so that the extracted components are synthesized with a random number particular to each entity so as to generate a secret key of each entity.