PURPOSE: To equally impart the control right to plural interruption processing logics by changing the priority of an interruption control table when the interruption processing having high priority is completed.

CONSTITUTION: When the interruption of a channel A is produced in the state I of an interruption control table so that the priority is imparted in the order of interruption channels A-D, the priority of interruption is set as B-D and A, that is, the lowest priority is given to the channel A (state II). When the interruptions of both channels C and D are produced simultaneously in the state II, the channel C having higher priority than the channel D is processed. Hereafter the interruption priority is set as B, D, A and C. Thus, the control right can be delivered equally to plural interruption processing logics. Thus, it is possible to eliminate the occurrence of an under-run error or an over-run error.