PURPOSE: To reduce the transfer data volume for remote retrieval in a distributed relation data base where duplicate data exist by horizontal division extraction.

CONSTITUTION: When a horizontally divided partial copy exists in the distributed relation data base as shown in the figure and a system 2 requests data satisfying a condition C2 of T1 to a system 1, all data is not retrieved from T1, but data D1 satisfying the condition of the product between conditions C1 and C2 is retrieved from T2 of the system 2 by the system 2 and data D2 satisfying the condition of the product between NOT of the condition C1 and the condition C2 is requested to the system 1, and thereby, the transfer data volume of data D1 is reduced in comparison with retrieval of all data in the system 1. Consequently, the transfer data volume for remote retrieval is reduced to reduce the transfer cost and the response time.