PURPOSE: To detect quickly the fault of a main controller and to utilize a POS terminal line efficiently by allowing the main controller to set a patrol polling interval to a subcontroller and a POS terminal equipment in a different length mutually.

CONSTITUTION: The sending interval of the patrol polling signal fed from the main controller 11 to the subcontroller 5 is made shorter than the sending interval of a patrol polling signal sent from the control section to the POS terminal equipment 4. The patrol polling signal is outputted from the main control section to the subcontrol section and the POS terminal equipment at a different time interval by the said means. That is, the polling signal is sent at the interval of, e.g., 2sec to the subcontrol section and the patrol polling signal is sent at the interval of, e.g., 10sec to the POS terminal equipment. Thus, the down detection time to the control section is reduced and a quick backup operation is ensured, while the line is utilized efficiently at the POS terminal side.