A dynamic load balancing method allowing a transaction processing load is balanced among computers by using estimated elongation rates is disclosed. In a system composed of a plurality of computers for processing transaction processing requests originating from a plurality of terminals, elongation rates of processing time for respective ones of the computers are estimated, where an elongation rate is a ratio of a processing time required for processing a transaction to a net processing time which is a sum of CPU time and an input/output time for processing the transaction. After calculating load indexes of respective ones of the computers based on the estimated elongation rates, a destination computer is selected from the computers based on the load indexes, wherein the destination computer having a minimum one among the load indexes.