PURPOSE: To suppress the frequency of input/output operation on an auxiliary storage by eliminating the need for a saving auxiliary storage area as an extra computer resource.

CONSTITUTION: An update control means 1 performs two-dimensional control over a page set 21 by a generation-1 external page set 31 and a generation-0 external page set 32 according to indications of a program part saving means 2 and a program part reloading means 3 by using an external page mapping table 50. A reloading unnecessary page specifying means 4 specifies a reloading unnecessary page at the point of time when a program reloading point is declared. The program part saving means 2 makes an indication for holding an external page map to be reloaded at the program restart point declaration point in the external page mapping table 50 and the program part reloading means 3 makes an indication for reloading the page set 21 other than the reloading unnecessary set 22 according to a reloaded object external page map at a program reloading restart request point of time.