PURPOSE: To improve input/output (I/O) processing performance when an input/ output interruption request is accepted from a peripheral equipment which has a different speed by varying a sequence after the acceptance of the I/O interruption request according to respective channel ports.

CONSTITUTION: An I/O 1 consists of an I/O control part 2 and three I/O channel ports 3. Signals indicating the channel number of the channel ports 3, received by the accepting circuit 20 of a control part 2, varies in value according to the channel number. Consequently, when a port having a short control sequence is accepted after a port having a control sequence extending between two clocks is accepted by interruption, sequence operation is delayed by two clocks. Thus, and overlap of control sequences is avoided. Namely, the I/O processing performance when an interruption request from a peripheral equipment having a different speed is accepted is improved.