To use a same interruption number in hardware interruption and software interruption between difference personal computer kinds.

A hardware interruption processing program with an overlapped interruption number is preserved in another memory and the interruption processing program to be emulated is assigned to the address of an interruption vector. An interruption service register is read at first in the interruption processing program. Since information for discriminating a peripheral device under an interruption processing at persent is stored in the interruption service register, it is judged whether or not interruption is the one from a hardware. At the time of no, the software interruption processing to be emulated is executed based on the interruption vector. At the time of interruption from the hardware, the hardware interruption processing preserved in another memory is executed. Thus, software property is effectively utilized.