PURPOSE: To enable replacement with a new kernel still in an on-line state without stopping a multiprocessing system.

CONSTITUTION: Processor devices 11 and 12 are equipped with migrating means 21 and 22 which migrate processes and rebooting means 25 and 26 which perform rebooting operation by using a kernel stored in a main storage device. The migrating means 21 of the processor device 11 which operates with the kernel stored in the main storage device 16 migrates a process that is being executed to the processor device 12 and the rebooting means 25 performs rebooting operation by a new kernel stored in the main storage device 17, and, the migrating means 22 of the processor device 12 migrates a process that is being executed to the processor device 11 and the rebooting means 26 of the processor device 12 performs rebooting operation by the new kernel stored in the main storage device 17, thereby replacing the kernels of plural processor devices without stopping the system.