PURPOSE: To improve the speed of processing and operability as a computer system remarkably by performing the interpretation and the execution of a program written in host program language efficiently.

CONSTITUTION: When saving a program Pk in a file area F, values e1Wem for steps S1WSm are so rewritten that values L1WLm of pointer 5 of steps S1WSm in the file area F indicate absolute address in the file area F of next step. The difference between the leading address of the program Pk in the file area F and the leading address of execution area E is calculated. The values f1Wfm in the file area F can be determined by adding the difference to values e1Wem in the execution area E of pointer 5 of steps S1WSm of the program Pk.