PURPOSE: To eliminate the need for a read-only memory for an initial program by loading the initial program for a slave processor in a common memory that the slave processor can access, and reading the initial program out of the common memory by the slave processor and executing it.

CONSTITUTION: The initial program is loaded from a boot ROM 14 to initialize a main storage device 3, and a system program is loaded from a file device 10 and stored in the main storage device 3. Then the initial program of the slave processor 6 which is stored in a file device 10 is loaded to the common memory 5 of a multiprocessor system 13. After the loading, respective reset flags provided corresponding to slave processors 6 are all cleared. Consequently, all the slave processors 6 perform power-ON resetting processing, make reads of the common memory 5, set in power-ON resetting interruption vector addresses, for instruction fetching, and execute instructions and end.