PURPOSE: To reduce the labor required for production of a patch file and at the same time to facilitate the control of the patch file by adding the valid revision information to the patch data for a load module.

CONSTITUTION: A load module 22 is loaded into a main storage 7 from a load module file 2 contained in a program medium 1 via a load means 5. A patch means 6 reads out a revision 21 and decides the presence or absence of the patch data remaining in the file 3. If the patch data remains in the file 3, the valid revision information 32 is read out of the file 3. Then the patch data 31 is patched as long as the revision 21 is held within the range of the information 32. The data 31 is not patched if the revision 21 is not kept within the range of the information 32. Thus it is possible to produce a patch file with a single patch file for a load module of plural revisions. As a result, the labor for production of the patch file is reduced and at the same time the control of the patch file is facilitated.