PURPOSE: To restart a control system at a high speed by setting up a flag to a register when a program is down-loaded after application of a power supply and checking the presence or absence of the flag when a terminal equipment is restarted.

CONSTITUTION: A terminal equipment 1 is provided with a program identifying register 5 which is initialized only at application of a power supply. A flag is setup to the resister 5 when a program is down-loaded after application of the power supply. Then the presence or absence of the flag is checked when he equipment 1 is restarted. If a program is already stored in a storage means 7 of the equipment 1, only the necessary data is requested to a controller 2 without down-loading again a program to the means 7. Then the warm start is carried out. Thus the restart of a control system is attained without down- loading again the program and the waiting time of an operator is shortened.