PURPOSE: To provide a system call function processor capable of acquiring error information inherent in a simulation system if necessary while maintaining an original interface in respect to processing for simulating the execution of a system call function in the 1st operating system of a computer by the 2nd operating system.

CONSTITUTION: At the time of executing simulation, a simulation part 2 transfers a restoration code regulated by the 1st operating system to a calling program in order to return the execution result state of a system call function to the calling source, acquires information indicating a state detected by the 2nd operating system 1 at the time of executing simulation and transfers the acquired information to an error information processing part 3 as error information 4. When an error reference function is called, the processing part 3 transfers information prepared based upon the error information 4 to the calling program.