PURPOSE: To decrease the capacity of a program storing part by eliminating the need for previously program storing operation.

CONSTITUTION: A program start-side system 1 which starts a program has a program storing part a15 which is stored with plural programs, a program storing information part a14 which holds its state, a program start control part 12 which starts the program by judging whether or not the program is stored in the storing part a15 when a program start request is generated from the contents of the storing information part a14, a program storing controlling part 13 which stores programs on other systems in the storing part a15 of its system according to the indication of the part 12, and a control program a11 which controls the whole starting-side system 1, Then the necessary program is supplied from a program supplying-side system 2 at a request from the starting-side system 1 and when a program which is not stored in the storing part a15 of its system is requested to be started, the program is automatically stored; when the capacity is not enough to store the program, unnecessary programs are deleted to secure the capacity.