PURPOSE: To perform high-speed data transfer and to increase hardware without changing the basic conception of microprogram control, by bringing an interface signal under the control of the hardware.

CONSTITUTION: An interface signal for a host device is brought under not microprogram control, but hardware control. For example, a data transfer request signal is inputted to a set signal line 11 to set a flip-flop 12, whose set outputs is ANDed with a signal from a signal line 27 through an AND gate 13 to set a flip-flop 14. Then, the set output of the flip-flop 14 puts a driving circuit 15 in operation to request data transfer over a channel and at the same time, a flip- flop 12 is reset through a signal line 22 and an OR gate 16. Once the channel accepts the data transfer request, the set signal of the flip-flop 14 is ANDed through a signal line 24, a receiving circuit 18, etc., to set a flip-flop 21.