PURPOSE: To grasp and analyze the operation of software at the generation of a fault and that of a microprogram level simultaneously by interrupting a microprogram in executing to start the execution of a routine.

CONSTITUTION: An interruption is generated by an external switch 6 to start the execution of a microprogram for recording information stored in a main storage device 1 in a file device 8. The contents of a microinstruction address register 2 and various registers are recorded in areas previously secured in the device 1. Whether the device 8 for recroding the information is usable or not is discriminated, and if usable, the microprogram and all data in the device 1 are recorded in the device 8 through a data bus 3. Thus, another microprogram completely different from the microprogram analyzing and executing the software can be forcedly started by the operation of the operator.