PURPOSE: To constitute the system so that another designated OS (operating system) can be operated from each OS by providing a reading means for plural OS's, an OS switching request receiving means, a control means and a control information saving means for the OS which is currently operated, etc.

CONSTITUTION: By a plural OS reading-in means 1, plural OS's which are desired to operate on the same system are read in at the time of start of the system. Subsequently, from the OS which is being operated, an OS switching request for designating the name of the OS to be operated in the next time is received through an OS switching request receiving means 2, or a request of the system end is received. When the received request is an OS switching request, an OS control information saving means 4 which is being operated is executed and control information of the OS which is being operated is saved, and subsequently, an OS control information resetting means 5 is executed and control information of the OS to be operated in the next time is reset. Next, an OS continuation operating means 6 is executed, and by switching from the OS which is being operated, a transfer operation to the OS which is desired to operate in the next time is executed. In such a way, the other designated OS can be operated from each OS.