PURPOSE: To reduce input/output operations from a second-order storage device and to enable high-speed retrieval.

CONSTITUTION: The registration information of a communication node address to be stored in a second-order storage device 3 is arranged based on a hash value 7 by calculating this hash value 7 from a communication node name as a retrieval key 5. The registration information is stored while being divided into plural blocks. Thus, a grouping means 1 divides the registration information into groups by performing hashing to the hash value 7, calculating the second hash value and performing grouping based on this second hash value. The registration information divided into groups are selected by groups and stored in the respective blocks by a storage means 2 by groups. The relation between these groups and blocks is managed by a managing table 4.