PURPOSE: To avoid reporting the abnormal interruption to the higher-rank side from the unused device and thus prevent the lowering of function of a control device, by accepting the interruption signal of the device that is registered with VARY-ON and blocking the interruption signal of the device that is excluded with VARY-OFF respectively.

CONSTITUTION: The VARY-ON/VARY-OFF information is transferred to the decoder 4 from the interface part 2. The VARY-ON information turns to the set signal (a) and the device number (c) or (d) to drive the FF9 or 10 via the AND circuits 5 and 7 and then sends the on-output to the AND circuits 11 and 12. Then the device interface 13 receives the interruption signal (g) from each device, and the interruption signal (e) or (f) is delivered via the circuits 11 and 12. On the other hand, the VARY-OFF information turns through the decoder 4 to the reset signal (b) and the device number (c) or (d) to drive the FF9 or FF10 and then sends the off-output to the circuit 11 or 12. The circuit 11 or 12 does not work, and as a result, no abnormal interruption is reported to the higher-rank side form the device which is not used. Thus the lowering of function can be prevented for the control device.