PURPOSE: To improve the throughput of the whole system at the time of DMA transfer by inserting proper weight numbers by devices at the time of DMA operation between I/O devices which differ in access speed.

CONSTITUTION: The wait numbers by the I/O devices are set in a register 21 in advance by using a CPU. In the DMA, a decoder 22 detects I/O device in operation and reads the wait numbers corresponding to the detected devices out of the register 21. A wait signal generation part 23 generates wait signals according to the read wait numbers, thus generating optimum wait signals for the individual devices.