PURPOSE: To prevent power-off due to erroneous manual operation by not turning off a power source regardless of the power-off indication of a terminal controller in the case of the existence of a terminal equipment being in the operatable state.

CONSTITUTION: A terminal equipment state monitor part 14 monitors the operation states of terminal equipments 21 to 23 to confirm the number of operatable terminal equipments. A power control part 12 confirms the number of operatable terminal equipments of the monitor part 14 when the power-off indication is given to a power-on/off switch 13; and if this number is 0, the power-off indication is issued to a power source part 11. If there is at least one operatable terminal equipment, the power-off indication is rejected. For example, when the terminal equipment 22 is in the operatable state, the monitor part 14 confirms it by periodical polling to terminals 21 to 23. When power-off is indicated with the switch 13 by an operator, the power control part 12 detects the existence of the terminal equipment 22 operated at present to reject the power- off indication.