PURPOSE: To efficiently store programs duplicated partially in functions in an auxiliary storage device when there are the programs having the duplication functions.

CONSTITUTION: Plural modules 23D, 23E, 23F... and description files 221, 222... are stored in the auxiliary storage device 21. When an execution program 272 for a function D and fa function E is generated, a program read means 26 accesses the description file 222 to read the two modules 23D and 23E out, and they are merged in a main storage device 25. Consequently, the execution program 272 is generated and executed. When an execution program 271 consisting of a function F and the function D is generated, two modules 23E and 23F are read out and merged. At this time, the modules 23E is common, so the storage in the auxiliary storage device is made efficient correspondingly.