PURPOSE: To improve the availability of a memory and to shorten the function loading time by using a function group file loading means and a function reproduction means to define the dummy functions with the same names of those functions given to users.

CONSTITUTION: A memory 1 contains function areas 11, 12,... and a dummy function name equal to the function name given to a user is defined in each function area. Then a function of the same name as that stored in a function group file 2 is loaded into each function area via a function group file loading means 3. Then the function stored in each function area is started by a function reproduction means 4 in the form of its original definition.