PURPOSE: To omit artificial operation and monitoring, by residing a parameterized position to be controlled in a control module and advancing step by step a control parameter to the next position by monitoring the selection completed condition and responding work changed condition by means of a timer whenever control output of one position is made.

CONSTITUTION: When a bath control switch is turned on and control registered in a parameter is started, a control module sends a control request to a transmitting-receiving module. When receiving the control permit of a pertinent route from the transmitting-receiving module, the control module sends a control code (selecting and operating commands of secondary stations and apparatuses) to a secondary station through the transmitting-receiving module. At the control module, time-out detection 13 is performed by taking the waiting time for three cycles from the control output to the change in responding work into consideration at maximum. When the change in responding work is recognized, it is considered that the control has completed and the next position parameter 15 is loaded to start the operation again from a new control request. When time-out is detected, an inhibit signal is sent to a control code distributor 14 and its control is temporarily cancelled, since occurrence of abnormality, etc., is considered in the transmission circuit.