1. A prefetch system in a computer system having a processor, a cache memory, and a main memory, the prefetch system comprising: a buffer provided between the cache memory and the main memory adapted to store at least one previous transfer request address for a case in which data requested by a data load instruction issued by the processor are not found in the cache memory and said data are requested to be transferred from the main memory; means for comparing said at least one previous transfer request address stored in the buffer, said at least one previous transfer request address plus a constant, and said at least one previous transfer request address minus the constant with a present transfer request address; and transfer-requesting means for generating a data transfer request which designates a prefetch request address equal to said present transfer request address plus a variable set by software and for sending the data transfer request to the main memory if the result of at least one of said comparisons is true.