The present invention is to provide a system capable of preventing an increase in load even if the amount of data increases. Upon receipt of a retrieval request, a main control part specifies, from a first customer table, row numbers adapted to the retrieval request. Then the main control part determines the range of data to be retrieved in a second customer table according to predetermined computational logic from the row numbers specified, the number of rows capable of being recorded in the first customer table for each customer, and the number of rows capable of being recorded in the second customer table for each customer.