PURPOSE: To prevent a device from stopping without preparing any error report to the external device by forming an error processing routine to be processed by an OS into a firmware, developing it in a CPU and a diagnostic processor and performing the error processing at the occurrence of the error in a main memory.

CONSTITUTION: When a memory area 103 in the main memory, especially an OS area 104, is destructed, a CPU100 is recognized of it via a main memory and CPU interface 102. Then the CPU immediately transfers the control to the error processing routine present at a firmware 107 via a firmware 101 incorporating the error processing function and a diagnostic processor(DGP) and CPU interface 109 to perform the processing such as preparation of the error report. Then the CPU100 once returns the control to the OS to perform the processing of proceeding with the operation of job making good use of a little resource when the destruction is restricted to partial area.