In a data base processing method including a central processing unit for analyzing a plurality of queries made from a plurality of users so as to determine an internal processing procedure with respect to a data base, and for performing the internal processing procedure; a secondary storage for storing data capable of being shared by each user; and, an input/output controlling processing unit including at least one cache storage, for controlling a transfer of a plurality of records which are required for input/output processing operations between the central processing unit and secondary storage. The data base processing method is featured in that a decision is made whether or not a prefetching operation is carried out at a start of an input/output processing operation by judging the internal processing procedure which has been formed by the query; a retrieval range into which a record to be fetched has been stored is formed when the prefetching operation is performed; and, a prefetching record number is determined as an input/output processing demand unit, taking account of an access characteristic of the internal processing procedure and also a system characteristic containing a size of the cache storage, a performance, of the central processing unit, and a traffic of the input/output processing unit.