PURPOSE: To perform down-load without increasing burden on a host system even when the number of terminal systems is increased, and by shortening the service stopping time of a communication line, and without requiring maintenance by a person.

CONSTITUTION: The host system 1 is provided with a program data base 3, a program transmission processing means 7 which performs the down-load of program data on the terminal system 2, and a restoration data transmission processing means 20 which performs the restoration processing of data not received by the terminal system 2. The terminal system 2 is provided with program data bases 15, 16 in which the program is stored, a restoration data reception processing means 21 for the data from the restoration data transmission processing means 20, and a program reception processing means 12 which receives the program data from the program transmission means 7 and also, stores the data received by the restoration data reception means 21 in the program data bases 15, 16.