A value of the number of prefetch words is preset by a master device 50 in a number of prefetch words setting section 14 of a slave device 10. The number of prefetch words refers to the number of data units sequentially receivable by the master device 50 at a time from the slave device 10. When the slave device 10 receives a read transfer request from the master device 50, a prefetch control section 13 reads from a memory 15 contiguous data units having a quantity equal to the value of the number of prefetch words, and then writes the contiguous data units into a data buffer 12. A bus interface 11 transmits the contiguous data units stored in the data buffer 12 to the master device 50.